We too had an area in the centre of the van that was "spongy" when our van went for service last year. The carpet does need to be lifted to do repair work, and any gaps on underside of van need to be taped up, else the chemical just runs straight out! Holes have to be drilled at regular intervals to allow chemical to be inserted. We ended up asking the workshop to do the job for us and were very glad we had, when we learned of the problems an experienced caravan repairer had, doing the job for us- he ended up having to use 7 kits to solve the problem!! so I would think twice before you tackle the job yourself.We now have an extremely solid floor!