do not think basement sealer would work. it will probably break down over time with salt water. epoxy and some sort of fiberglass application? might want to look into that more.
i went to my local sherwin williams and told them the application and they hooked me up with a 2-part marine epoxy. The rep told me it would be best because it allows for some expansion/contraction and still not crack. My tank has been up and running over 2 years now, no problems. cost $90 for 2 gallons.