There's not been a ton of experimentation with drylok as a tank sealer. It's not designed to hold standing water but there have been reports of it being used like that successfully.
Check out monsterfishkeepers.com. There are some failures and some one or two year old successes. From the small amount of reading I've done, it looks like the initial construction of the box is very important and that gaps and weak seams will surely lead to a failure.
I'm contemplating trying this out on a very small test box just for fun. Using something like 1/2 inch MDF lined with several coats of drylok, maybe with some geotextile fabric in between some coats for added reinforcement and filling it water and seeing how long it lasts.
I say go for it as long as you're prepared for something to go wrong!
In my paludarium build (see link in my signature) I used fiberglass and epoxy for all the submerged areas and epoxy for most of the rest. I used drylok on some of the top braces and center brace, figuring that it would only have to be a humidity barrier and it still didn't hold up particularly well. A little bit of water got through, causing the plywood to swell and the outer layer to start peeling off. I ended up stripping those sections and resealing them with epoxy.
I think drylok doesn't penetrate deeply enough into the wood to form a truly waterproof barrier.