Solved my shell on flooring replacement problem.
I used a 4x4 timber and jack post between the ground and the ceiling to lift up the shell a bit. I have one section of belly pan removed that gave me access to the ground.
We managed to wedge the plywood flooring between the frame and the c-channel with the help of my partner, some pry bars, and a sledgehammer. Sounds dramatic but it really wasn't too much brute force needed.
ONWARD!!!
Flooring section installed - with plywood pieces screwed and glued in the edge to join and support the next flooring section.
The funny looking thing sticking out of the floor is a ground line attached to the frame for my
12V electrical system.
c-channel and fastener screws