[DK on the road]

This was a dream of mine also.  Beautiful work and detailing by the way. You may have engineered all of the following, but for future pit fans, consider the following 3 concerns not mentioned.

1) Air ventilation of a confined space. Consider an air evacuation fan to turn on before entering the pit. Gasses you shouldn't breath are heavier than air and gather in low places, granted your head is generally above the ground line, its gases from a sewer dump line (sewer gasses), oils, gasoline, cleaning products etc that gather in pits. It doesn't take much of a fan to transfer air in and out before entrance and while working in the pit.  A permitted pit would require this.

2) The soil type, concrete pad thickness and reinforcement is important. The concrete pad looked significant, but subsidence, settlement and cave in is a factor if not all points are reviewed and engineered. The weight of the Coach, where the wheels sit in relation to the center of the span of the pit, vs the horizontal support or resistance at that point all should be considered.

3) Make the covers lockable. This can be a attractive nuisance if the ventilation fans are not automatic and a child (which have more sensitive lungs) enters this confined space. This is of special concern because it is outdoors and you could be traveling and away from it. Look at it as if it were an swimming pool, instead of water, possible poison gases.

Both of these issues, many times deadly, come from a part of the world I left.  Don't ask me how I know...I will go to tears. Actually you can ask me, I'm better off mentoring and training to help avoid failures in heavy civil construction