I've been trying to find a way to deal with these issues also. I have a 57 Overlander single axle. I'm ready to lift once the weather gets a little dryer. I think my answer is a combination of the above and a few other things.
First: With the interior gutted I'm going to create a template of the floor out to the edge of the C channel. See Frank's Trailer Works http://frankstrailerworksblog.blogsp...-this-tip.html
Next use that template to create the outside support like Darkspeed (1 1/2" square tubing) and weld it to the frame. My hope is this will make sure I maintain the same "footprint" when resetting the body, with the bonus of separating the plywood floor from this joint.
While the body is off use my flange tool to create the off set to the bottom of the exterior panels that go below the existing C Channel. This allows the panels of the belly pan to slide in between the exterior panels and the new tubing support. (see diagram) I know I can't do this everywhere. I've pulled some of the belly pan off. Some panels don't go below the C Channel. The end caps screw into the plywood so I could attach those to the tubing support. On those panels that don't extend below the C Channel I could add a Z channel between the exterior panel and the C Channel to get the length.
I would blind rivet the top of the belly panels to the new tubing support so either panel can be removed without affecting the adjacent panel.
The downside I see is having to wait and attach the new belly panels after all this and not when I can have the frame upside down.
Welcome your thoughts on this: