Got my floor fitted!
I didnt use clecos, I drilled holes at every tube intersection to start and then riveted it down at 4 corners before drilling all the other holes. Drilled the 4 rivets out to clean up/deburr then sikaflexed the chassis plonked the sheet on top and riveted all round.
4 and a half hours to drill and deburr 264 holes then PU and rivet 264 rivets. Phew.
Cheers
Stot