I'm about ready to put the body on the frame next week.
1. Does anything (such as welting) go between the rear of the body and the rear (fuel tank ) apron.
It seems like it would be metal on metal and would squeak or rattle with out something there.
2. I have installed webbing on the splash aprons (under the apron between the apron and frame) along the full length (see picture). It sees like it would be a waste as the splash apron does not rest on the frame for the entire length.
Any help is appreciated.

You can use some heavyweight roofing felt paper.

Thanks for your reply. I appreciate your help.

Any help with the 2nd question?

Bump

I am not aware of any cushioning material between frame and side aprons. There were water proofed fabric pads at each body bolt between the wood and frame or splash apron.