I think what you want to use is a rivnut. It installs much like a rivet, once installed you can bolt your seat or whatever directly to the floor. I have used these extensively on my jon boat, and have a seat installed using them and they hold just fine. They are great in locations where you can't access the backside of the install site - jon boat ribs for instance.
Link to inexpensive tool and comes with rivnuts.
45 Piece Threaded Insert Riveter Kit
Also google 'rivnut' and 'how to use a rivnut'