I see Lance as being a quality built trailer as it is CNC constructed with tight tolerances. Stout and Rugged? No. Their frame has many relief holes to reduce weight. Probably precisely engineered for its intended purpose which is not off roading. I have a friend who had one and wasn't allowed to put a bike rack out back because the frame wouldn't handle it.
Check out BigFoot as they meet most of your criteria. They do have low ground clearance so would have to be raised. The cabin is a vault and they are 4 season. The frame on mine was 1/4" thick 2" x 5" box section full length and double stacked over the axles. I've seen a lot of larger trailers with not near as much frame. No rubber roof, no leaks. Extremely high quality of construction and a corresponding price.
