I had the opportunity to see a new starcraft, aruba travel trailer at an rv show near by here. I was fascinated with their very simple solution to adding slide out space to an rv. They use it to create a slide out queen bed that is just slick.
It is manually operated
. When you park, you put a couple of folding angle brackets into sockets in the bumper and the back of the unit, forming the slide tracks. The unit extends with a gentle pull on the box.
If you have a chance to see one, go look at it. It should be simple to duplicate and looks quite durable. No electrics, cables or hydraulics to go bad. Also looks as though it could be adapted to use on the side of the rv as well (knowing what clever people skoolie converters tend to be
If you google starcraft aruba in the image finder, you will get a few pics to get your interest going.