building a basking spot/hide

Im getting ready to build a basking spot and hide for my little guy who's missing his right feet. My questions are at the bottom.
This is from the beautiful dragons website, kind of paraphrasing it to fit my questions. Here's the website I took this from: http://www.beautifuldragons.com/Furniture.html

Supplies:. The following list is what I purchased at Lowes: 
Glue (I bought "Titebond" all purpose white glue because it works well with porous materials) cost = $3 
Polystyrene (I bought a 1" thick sheet that was 3 feet wide by 8 feet tall) cost = $6 
Tile Grout (I bought "Premixed Sanded Grout" by Mapei, white) cost = $7
Grout Sealant (I bought "Penetrating Sealer" by AquaMix) cost = $6 
Paint brushes (I bought 2 (1" wide) paint brushes for the grout and sealant) cost = $2

These are items I had around the house that I used: 
Toothpicks (can be wood or plastic, tYt?he thicker the better)
Sharp knife 
Butter knife or putty knife


 After several layers of grout, I applied the grout sealant and "threw" sand on it. I didn't have a lot of luck getting much sand to stick. I decided to paint over the grout and sealant with something called "Weathered Stone." It's a textured paint that is used to make something look like stone. And it worked really well!

Click to expand...

Now, my questions are:
Once the poly is cut and glued together, is there something that will help keep the grout on it? My fiancee used to set tile back in the day, and he said that adding a latex additive to the grout would help. Was wondering if anyone has used this method? I plan on building something that I can take out and wash off because my lil guy likes to poo on his basking spot. So I need to build something that can stand up to almost daily rinsing and weekly washing.

Also, is there a need to go farther than grout/sealant I.e. weathered stone paint/sealant ? Or is that just for aesthetics and additional texture? I would think that sanded grout would have enough texture to it to help with grip and "nail filing". Grout comes in a plethora of colors (he set tile in our old house using glow in the dark grout) so what would be the point of the weathered stone paint?

I want to make sure that what I build will stand up to whatever comes it's way with minimal need for patch jobs. So if anyone has anything they've done that worked well, im open to suggestions!! I want my little guy to have an awesome basking spot/hide. Thanks in advance!!