The kickstands of the bikes will gouge the paint. Use a bunch of old socks to slip over the kickstands and have at least 3 fastening points to tie down the bike ( 4 is better), keeps it from jostling.
Roll the bikes into the bed and onto a scrap piece of clean carpet, fuzzy side down. In a pinch use floor mats. Magnetic pan for oil drips is cool.
Most everything else will hide the new paint or scratch it up.
Old custom "rodders' of the mid-1950's used to put a white tonnue cover (tarp with snaps) over the bed to add a second color to the trucks' scheem and protect the bed paint.
The heavier the bike the more it will try and gouge into the bed.
john
