[Jack Houpe]

Morning Forest, thats a good idea aqua hot compartment normally warm, cut a hole and put a 12v fan on a thermostatic switch.  They make the rubber heated mats for lithium batteries to sit on thats another way to heat also. I buy my batteries from China and make what ever configuration by series and parrallel individual cells its much cheaper that way and add a BMS (Battery maintenance System). I built this one for my nephew in Surprise AZ it was a tight squeeze, its 200 amp hour @ 48Vdc, he wanted a battery for his golf cart that would last for miles. The other image is 600 amp hour at 12VDC we had in our Class B RV.