I ordered two 29" squares cut from 14 gauge steel to cover the holes that will be left from the roof exits. I just threw my tape up and measured enough so that there would be plenty of extra material. I think 16 gauge would have been fine, though. I think I'll use 16ga for covering up the window openings.
All the side panels are out of the interior, and I am about to start on the ceilings. I'll be happy to be done with rivet removal.
Oh and on another note- Rural King has a sale going on till the 13th. I need one new battery. I went in yesterday and the group 31 they carry is made by Exide and the sale brings the price down to $70!