None of the common sealers people use are truly water proof. To accomplish this, you'll need to use epoxy. Coating items in silicone is also an option, but it looks like crap and is hard to clean. I'd relegate this to items that will be submerged in water. Otherwise, epoxies dry inert and non-toxic, and will be more durable then practically any other sealant. The biggest downside is the difficulty of application, especially on a surface that isn't flat.
That said, you won't find anything easier to apply that offers more water resilience.
http://www.eti-usa.com/consum/envtex/envlite.htm
That stuff has a good reputation among cage builders.
There are things called epoxy paints. Not truly epoxies, and I can't comment much about their toxicity. However, they should offer a decent level of moisture protection, though not on the level of a 2 part epoxy. You can even find these in a spray can, though once again I can't comment on the level of toxicity. Though most any hard drying top coat will be inert (non-toxic) once cured. Epoxy paints should be easier to apply on an irregular surface...however durability will be a question depending on the product you use. The only epoxy spray paints I can recommend are the ones that mix the resin and the hardener as it leaves the can...I believe Rust-Oleum has a product like this.
You specifically mentioned "water proof" in your post, and sadly this pretty much limits your options. If you think you can get by with something that's just water resistant, then there are other options (polyurethane). I'll post more tomorrow.
Good luck with the project!
