[hbens]

So I installed Pioneer Mini Splits. My SCS units bit the dust. I opted for YN020GMF122M2E a 20kBTU outdoor unit and 2 12kBTU concealed duct models.    
I installed the two concealed duct units inside the current air return plenum. I wanted to make sure I had two separate cooling zones just like the original AC setup. I also wanted to keep the Aquahot for a second method of heat.     
I reused the duct to the rear of the coach      and 4" round insulated duct from Lowe's for the front. I also reused the thermostat wiring so I didn't have to pull new wires.
Each cassette has a manual thermostat I mounted in the curb side bay inline with the new thermostat inside the coach. I mounted the new indoor thermostats above the old ones.
I used 1" duct board from Lowe's to make ducts and close in the cassettes. I used a 30AMP lighted switch to control power at the outdoor unit     and the OEM circuit breakers in the panel in the wardrobe. In the curb side basement I wired up two outlets with the wires from that SCS unit.
The units came right on and blew good and cold. The issue I have is getting heat out of the basement when running the AC. We camped out one weekend in the Florida sun and the unit would not keep up with the heat. While stopped I kept the streetside door open which helped but wasn't enough. On the way home there wasn't enough airflow to remove the heat from the outside unit.
I added an electric fan to suck air out of the streetside basement door.      I controlled this fan with a switch mounted on the wall in the bay. I added a 120vac triggered relay to control the fan from the breaker box inside the coach. This way I wouldn't have to go outside to shut the fan off if I turned the AC off.
This fan wasn't enough so I installed another fan on the curb side to draw air in through that basement door. Both fans are controlled in the bay with different switches and the common 120vac triggered relay. Also, the curbside basement floor vent hole for the SCS unit is covered up now. The streetside basement floor vent for the SCS unit was covered with a grate and I use that to drain the condensation.
After a few hot days in the 90s I realized this wasn't performing well enough. I added two more 4" ducts to the front cassette, through a 4" to 2 1/2" Y connectors through the Aquahot vents below the cabinet under the salon window. This helped quite a bit. I reconfigured the duct for the bottom cassette and you can see the results here.     
I think I need to add additional duct from the rear cassette to help that work more efficiently. Doubling the front cassette ducts seemed to help that run better and improve cooling.
I shot my infrared thermometer in various places in the coach and I am shocked at the temps I found. The windows on the sun side are 110* on the outside and 98* with the shade down on the inside. The side of the coach was 130* below the passenger window, 125* on the black window cover on the outside. Inside it was 84* behind the roll up blind and the windshield curtain. I am looking at making body window covers for the rest of the coach to block the sun from coming in and boiling the inside.
Rubber freon lines are now available. They weren't when I ordered my units. I would definitely pay to use them instead of the copper lines.
This is a work in progress so there will be some changes and improvements in the future.
Thank you Richard for putting your eyes on my project, thoughts and ideas. And for outing me too...
Thanks to the others who have posted their mini split installs and those who responded to them. 

https://drive.google.com/drive/folders/1...sp=sharing Here is a link to the folder of photos I've taken so far.

[Jonestead]

Very thorough, well thought out and nicely executed 
As you discovered sometimes more is better
My SCS units had both intake and exhaust thru the floor and solid basement doors.
It seems as though Newell changed to door venting around 1998 so I assume they did that for better exhausting 
Without measuring, it looks like your door vent is larger than my floor vent, 
Have you experimented with forcing the exhaust thru the door like the SCS did with some kind of shroud/duct between the fan and the door?  
Seems like that would stop your airflows from mixing completely 

Just thinking out loud

[hbens]

Arch,
After seeing your shroud I'm considering getting some exit ducting made. I haven't secured the outdoor unit to the floor yet so there is some room to move it a little. It is only bolted to the 2X4s right now.
Getting rid of heat on the outside unit and getting enough airflow through the cassettes are 2 key concepts I keep thinking about.
I've been working on this project since the end of March. I think it took me about 6 weekends to get it to the testing phase. I did a lot of thinking and redoing some things. Then redoing my redoing.

One thing I was surprised about is the ease of access to the floor from the basement. Pulling the insulation board from the basement ceiling exposed the subfloor where I could see exactly where the 2.5" Aquahot ducts enter under the cabinet. I could also eliminate a turn in the 4" elephant feet ducts.
I'll think about this a bunch and consult some gurus before I do anything big or irreversible.

[Jack Houpe]

Summer is upon us and I think we will see many people switching out to alternate sources of air conditioning due to the age and inadequate parts supply of the old SCS units. Good to see people sharing pictures and information so it will help future conversations. Hank I'm glad you made the conversion I'm sure you will be happy camper.

I have venting through the floor and also the door is perforated, there are two rectangular vents on each side of the bay floor. I placed each compressor center of the aft vent holes with with the thought that would be intake air then the exhaust of both units going outwards toward the doors and other floor vent. My plan was to use the 1/4" double sided aluminum sign board to fit around the whole compressor and screwed to the walls to force the hot air from the compressors out through the door and the bottom vent closest to the bay door. If you have access to purchasing this product I highly recommend it, its strong and you can cut it with a skill saw, easy to build ducts with but not curved ducks and its plastic center so water doesn't bother it.  Of course I have not done that YET but its on the ever growing list of items to finish but I open one of the bay doors when in operation.

[Frankie4Fingers]

Any suggestions on finding a company who will do this sort of replacement for me?  One of my two basement units isn't working well and I would prefer a much stronger and more reliable system but I don't think I could do the work myself.

[hbens]

Corey,
Arch found someone to do some ductwork for his.
I did my install myself.
However, I'll be adding another outdoor unit and an indoor hanging in the bedroom running on 115v instead of the 220 the first setup uses.
I'm going to reconfigure my setup some but I haven't settled on a specific way yet. I got some input from Richard and I'm figuring out how to manage that as well.

My guess for finding someone would be to go to an HVAC place and talk face to face with them. I wouldn't just call. You and they can read each other and understand wants better that way. Translation can get lost over the phone.

[Frankie4Fingers]

Good suggestions.

Right now, one of my basement units works, the other makes bad sounds so it might just need a tuneup. I bought a portable unit for now because I am in St. Louis and it is 101 and feels like 114

[Jack Houpe]

Buy a 24k but 3 zone LG compressor use copper lines, put a 7500 btu in the bedroom a 12000 btu ducked unit over the refrigerator and a 12000 btu wall or art unit in salon. You'll be happy and done with it. No lost due to ducts and better CFM exchange of energy. I've done 3 systems like this and no problem it's extra work but worth it. If you really want to show off put another compete unit for the bedroom alone 12000 btu max then brag when the outside of the coach starts sweating.

[Jonestead]

Any suggestions on finding a company who will do this sort of replacement for me?  One of my two basement units isn't working well and I would prefer a much stronger and more reliable system but I don't think I could do the work myself.