I have used a sealant called Q Seal, that I use sealing saw cuts in concrete/asphalt when installing detector loops. I put some on my frnt tank 3 years ago and fixed all the cracks, splits and holes. The stuff is indestructable and stays flexible.I get it in tubes (1 qt ) from LIS Systems P O Box 1654 Athens TX 75751 1-800-964-0711. Tell J.R. that O C sent you. Great guy.Their min. is 2 tubes @ 17.10 ea.,but he may send one if you sweet talk him.If not PM me and I'll see if I can hook you up.