Here is another option for quiet heat. I installed one in an old motorhome in the 1980's. It worked superbly, but they are fairly expensive. I like the safety of a fully vented system, so you can close all the windows
without fear. The drawback to cats is they do not warm the air in the space, they only warm people and objects. The orientation of the install makes a difference. Ideally you would want the heater aiming down the center of your rig at your most frequently occupied area. In my 16' Scamp
side dinette floorplan that isn't possible. All other cats that I know of burn inside air, which to me is way to risky to consider.