ok im going to be building a new tank for my cats buying a busted 150 long tank cutting out the glass for the windows the tank will be 4x8x21 or 4x6x21 depending on how much room i have. hear is my question what do you seal it with i was thinking pond liner but the cat might poke holes in it, i was thinking fiberglass but your talking big money and lots of ventilation. but i am seeing people yousing a paint on apoxy to seal them how well does this work what are we looking at price per gallon were can i get it and is it a good long term sealer. o the tank will be framed with 4x4 outer rim with 2x4 studding 6"on center with a front rail of a 4x6 reinforced. yes i will be fiberglassing the corners and 3/4 plywood insert. thank you i really would like any advice i can git it is better then this thing springing a leak and rotting out on me as 3 of the 4 walls will be up against concreat walls