Bonding Block to Fiberglass Pool

[traderfjp]

need to bond concrete blocks to a fiberglass pool. The fiberglass edge that the block will be bonded to is not perfectly flat or level. I called Alliance that sells Gator XP which is a very strong polyurethane adhesive. The rep is saying that it can handle pool water and will bond to fiberglass. We are going to sand the fiberglass with 90 grit sandpaper to create tooth. This is a small pool, 12 x 25 and we want to use the best material. The guy who makes the coping suggests PL premium. It never really gets hard. The coping is about 14" wide and will over hang the inside of the pool by 1". I was going to set the block that isn't bonded to the fiberglass on roadbase. I didn't want to use concrete to allow for movement of the pool. Would we be better off using a flexbile thinset? I just don't want to have problems with the blocks popping off. The fiberglass edge that the coping would sit on is about 8". We laid it out and it dosen't come close to laying flat. I know that poly adhesive is not a gap filler and we will have some gaps. Also we live in NC on a mountain and it get below freezing and hot. Any advice is appreciated.