Hope someone chimes in on best-effort wooden beam to bridge between to roof vent openings to use as a lift point on your 31', I did not use that method...
Mine isn't the greatest thread match to your order of work but it includes some odd problem solving I dreamed up...
hey-yall-watch-this-shell-game
My every fifth Sunday project just saw me button up the wheel wells last weekend - when landing the shell back on the rebuilt frame/floor one must have a mechanism to 'stretch' the shell to get wheel well skirts 'taut', where the ribs sit/gouge into the flooring 'double-C-channel' provides extreme friction and it's easy <cough> to bolt things down too fast <cough>...