Do a search for 'riv nut' on google and it will come up with a few hits which explains the system.
A previous thread discussed the same issue - the best method to secure the floor panels. Would be worth having a gander.
http://forum.madabout-kitcars.com/viewtopic.php?t=113
PH also discussed the same subject on their kit car forum.
Cheers, John
Madabout-kitcars.com