I have used silicone and phenoseal chauking for my bathtub, but neither works. The silicone chaulking does not adhere to the fiberglass tub and the phenoseal chaulking cracks within 2 months. I tried filling the tub with water and sealing it while standing in it, but this did not help. Is there any other chaulking to be used in this application? Note that I am trying to seal between the fiberglass tub and marble tiles.