I finally got around to trying mine out on a recent camping trip. Worked pretty great. A bit annoyed that the pump can't be shut off with the shower control -- the pump runs even if you have the shower handle off with no water coming out. Pretty easy to get the temperature that you want and it does a great job at keeping it there. I have mine mounted in the bed of the truck. There is about an inch between that and my fridge, and on the other side about an inch between the wall-storage divider. So I would think clearances are pretty small and venting requirements pretty small if you trailer isn't air-tight.
I carry two 7 gallon reliance containers with me mounted at the back of the truck bed. Pretty easy just to drop the pump in the water container, but I need to make an attachment so I can leave the pump in and have it be water tight so that I don't need to take it out every time I leave camp. As for freezing temps, it says not to use it in freezing temps -- there seems to be no way to get all of the water out of the unit and with copper? heat exchanger, I would think there is some risk of bursting a pipe. Aside from that concern, cold shouldn't matter, you would just have to recirculate until you warm it up enough for the 40-50 degree temp rise.
All in all, nice unit. Wish it was a bit smaller and I wish it didn't have a built-in battery that takes up extra weight and space that I don't need.