Ok, as I said before I decided to fiberglass the entire water portion of the tank using West System 105/206 and lightweight Bondo brand fiberglass cloth. This will provide structural strength and an additional layer of waterproofing. Now that I've gotten the hang of it, fiberglassing is actually quite enjoyable... almost addictive according to my wife
If I had more epoxy and fiberglass I'd probably glass the entire interior but I don't want to spend the extra money and I certainly don't think it's necessary.
Here's a piece of cloth trimmed and layed out
Wetted out with an initial layer of resin. I used a bondo spreader to wet out the cloth and a small brush to do the edges
After it gelled I trimmed of the excess and then applied 2 more coatings with a roller to fill the weave. Here's the tank with the lower half all glassed up. It's almost hard to tell because of how clear it gets!