Don, if all you want are a couple "bumps" you can make your own by using a bowl, storage container, whatever that's got a shape something like you prefer. Use it as either a male or female mold. Slather it up with wax (Rupnow goes into more detail in his top thread, so similar procedure), and lay in/on some cloth/resin. Mark where you want them by going underneath and drilling markers for location to cut the holes you want to cap. Grind back the gelcoat and use bonding resin to attach the caps you've made. A little body work and you're golden.

Now, think about some other things. If I recall you think you want to have a rumble seat arrangement. Don't forget to think about the affect of a couple of "bumps". Depending on what you want and where it all falls in relation to footroom and seat placement, it may be more practicle to cut out a section of the floor in one piece and raise it the necessary amount. Again I'm just guessing here, so this is just a thinking exercise, but lets say you could cut a section 4" wide (actually front to rear of car) and say 25" long (across the width of the compartment) and just raise it say 1.5". If you're clean about your cut line you just form a dam around the opening, reuse the cut section as the "top" of your raised section, and glass in around the perimeter, removing the dam after curing of the new cloth/resin added. Part of this will depend on how you want to finish the floor for the future. As often happens you'll need to put down some sort of material, sheet metal, plywood, hardboard, whatever to give the appearance of a flat floor, unless you're happy with the look of a floor with "bumps", though your upholsterer won't keep you on his Christmas card list if you make his job too dificult.