Roy, I have one 80 foot car and six 67' cars including an observation. The floors are 1/8 " wood, looks like clear pine with the edges thinned down to about 3/32" I've been thinking of using 3/32 aluminum although it is heavier than the wood floor. AF floors from the plastic body cars are 1/32" and will slip into the Midgage bodies.
Typical car ends and underside detail on 80 foot body.