Living in a nomadic homes tends to involve a lot of time spent outdoors. Why else would you do so much traveling, if not to experience the places you go to?
At the end of the day, though. When you retire to your nomadic home, you find yourself doing a lot of sitting down, so some thought should be invested into making this as comfortable as possible.
There is some flexibility in both height and depth of seats, provided they relate to each other. In other words, the more depth you have, the less height and vice-versa. as a guide, the depth (front to back) can be between 16 and 22 inches (400mm and 560mm). The height can be between 12 and 17 inches (300mm and 430mm). So as an example of how to use that scale, it could be 16 inches deep by 17 inches high, or 22 inches deep by 12 inches high, or somewhere in between, provided the same inverse scale is used.
The back rest should be angled back by about 10 degrees. Straight back rests can become very uncomfortable, very quickly.
As has been pointed out to me by several long term house truck owners, the most comfortable seating on wheels, is the standard house hold couch. It’s a shame that house hold couch’s are not practical on most boats, they are used on some large barge’s and house boats, typically where they remain in sheltered water.
Another consideration when designing seating areas, is to make sure people can be seated without facing each other directly. Even facing at right angles can give the illusion of more personal space in what is a confined living area, which can go a long way in maintaining relationships with co-habitant’s.