Pictures! get some pictures up to help get our brain juices flowin'! This will give us buzzards an idea on what needs to be repaired and how big the job needs to be.
As far as the expanding foam goes, unless the repair job is huge and there's no saving the floor, it seems like a bad idea to me. you'd forever have to keep the boat inflated, the floor will be a large hard mass and probably will come out really lumpy and misshapen.
If the repairs not too big, I'd maybe try taking some strong thread and sew it through both sides of the floor. If you leave this thread loose enough, you'll still have enough room for an air chamber, but tight enough to help reduce the blow out. When done, patch both sides (maybe even twice) to fully cover the thread and your handy work.
If you try this, let us know how it goes, I've never done it before...