Those vinyl trunk mats are NOT good! You are right about that body sealer, once some moisture gets under it, look out! Got a leak and get moisture under your carpet, it will begin to rust.. Those old cars that came with the rubber (or is it sort a vinyl?) floor covering and not carpet, they rust pretty bad.
Every person that owns one of these old cars needs to see first hand how rust forms. I don't mean the obvious. Buddy of mine had been a body man for 10 years. He pointed out to where he replaced a rear quarter and overlap the patch or original metal TOO much. This was on a 70 roadrunner he had bought new. It had started to bubble there some years later. He explained a butt weld was not in his cards, but he should have only overlaps it just as little as possible. Back then there was no weld thru primer to help either.
Rust never sleeps, but we can do all we an to slow it wayyyyyy down!