And the results are in...
Well it's been a while but since I figure all knowledge gained needs to be shared, here goes:
Started with an old "udisco deluxe hypalon raft" which had a standard floor (SF)
I also had a drop stitch floor which I acquired from some other boat. (having this for cheap was the key to this project)
After talking with some people, decided the best (easiest) course of action was to stuff the floor into the boat and punch holes in the floor to drain. This prevented any issues with trying to mate the old floor to the new, or remove the old floor and lace in the new one.
We couldn't lace the floor in because as it turns out the boat is too small (about 13') for this particular floor (need a few inches all the way around for a strip of grommets). After some deliberating with long time boaters and river rats, we decided that since the fit was so tight, and the thwarts were staying in, that the floor was going to hold itself in the boat just fine.
I glued about 14 patches, 3" diameter, on to the outside of the floor, along the main tubes, about 6 inches from the seam where the floor meets the tubes. Once those dried (overnight when using shore adhesive 1 part) I went back and using a 1" punch tool put holes in the center of each of the patches on the floor.
Next, I stuffed the floor into the deflated raft, pumped it up a little to get it to take shape and make sure it was aligned and then pumped up the raft.
The floor fits pretty nicely on the sides of the boat. It's a tad long for this boat though and the front and the back are definitely curled up a little while it's in there, not too bad though, maybe an inch at each end.
The end result is an old, ugly gray raft that bails all on its own. I've taken it down the Main Payette once so far, and the Cabarton section of the North Fork of the Payette twice. So far no problems other than a slow leak in the front thwart and what may or may not be a really slow leak in the main tube (baffles are gone in this thing so when I say main tube, it really is)
Sounds pretty ghetto I know - and it is - but it was cheap and it works. Also I learned a lot about gluing hypalon, which I've done plenty of while reattaching seam tape etc.
Once I get the motivation I will post some pictures of "Lady Bertha" so the locals can laugh when they see her/me.