Including the radius face panels would make a kit like this very hard to pass up for a novice. And if those are included in a kit, the below design (as a non tub version) IMO would be one of the most feasible "conventional" tear designs to go commercial. It would be a very compact unassembled package for most economic shipping compared to using larger radii pieces.. No plywood radius bends to make yourself, and a flat hatch. That's about as simple to build as you can get.

Inner fenders.. Might be beyond the scope of a floor sleeper, but might be a necessity for doing much with a HF frame. I believe you already have an inner fender option for the tubs, but would it easily adapt to a non tub kit?
Thoughts on using VHB tape for adhering the fg parts together?