You can try covering the fronts more, I'm sure that wouldn't hurt. Just be prepared to buy new ones with a smaller opening (either caves or the plastic RBI ones) if he doesn't like the large front openings. You can also use cereal and other boxes, just cut the bottom out and cut an entrance "hole" with scissors. You will want hides that fit tightly to the BP to help it feel secure.
If you want to use the polycrylic, I'd suggest applying it in several thin coats, letting each coat dry very well between applications. I think I did 3 coats on my large grapewood piece.
If you are looking to buy more wood pieces for him in the future, you can look for manzanita, mopani, and ghost wood, as well as cork bark. All of these hold up to moisture well. It is a good bet that if a piece being sold online is not labeled specifically with one of these names that it is grape wood.