Well, I ended up using Plasti-Dip since it was the easiest to find locally. Let's see how it'll hold up over time. I applied 2 coats of Plasti-Dip and 1 coat of S2 Epoxy sealer over top. I filled up the planter yesterday with water and added the water lilies. They seem happy.
Rubra
Helvola
I call this Phase 1.
Phase 2 will have a smaller planter (mounted over top of the larger planter) with a water tap to pour water into the bottom planter. I still intend to add a solar pump eventually. I found a 12V UV sterilizer/pump that should work great for this application.
http://www.aa-aquarium.com/showroom4.php?id=156&level=1