I use the truck cap seal stuff from Home Depot, at least on the floors panels and transmission tunnel; I haven't had to remove the seat box yet. It's the thinner gray stuff. It squishes and fits nicely. No leaks yet. It also does a decent job of sealing old seat bracket holes under thicker mats.
"Every normal man must be tempted, at times, to spit on his hands, hoist the
black flag and start slitting throats." - H. L. Mencken