We change drivers every couple of hours, STOPPED either at a rest area or on a wide shoulder. That gives us both opportunity to use toilet without moving around. We stay belted in most of the time. Sometimes whoever is in the nav seat will get up to use toilet or grab a snack. This is done in consultation with the driver who has final say because that position has situation awareness.
We certainly would not be heating anything while underway or lying on the bed or sofa. When we have grandkids with us they trade off the nav seat with non driver and we set up the belts on the sofa - for what ever they are worth (very little in my estimation, but maybe better than nothing). Coach has no separate recliner or dinette booth with seat belts.