The bounder has or had a cover where you put the sewer hose and two or three 1/2 in holes for any water to drain out.
I thought about it on a trip to Fla a few years ago when daytime high was in the teens, of putting piece of duct tape on the holes, temporarily. I didn't and all was good. There is power in the wet bay, 12 volt for the light and water pump.
120 is on the other side. Not too much of a problem to do some wiring and plugin there. Only would have to run the inverter going down the road.
A 120 bulb will operate on 12 volt, but I haven't done the math to see if there would be problem. Probably not.
Real solution would be a GFC equipped very small heater and fan,on either 12 or 120. On 12 volt, it would require at least 10 gauge wire from a DC breaker.
Don't know if there is an extra or space for one or not, but just bit more work if not. Just don't want too much juice from alternator, so I guess that woule mean Inverter and do the math on draw.