Hi friends. I'm making my first book case, and I am staining the backing (some cheap 5mm underlay plywood). I'd like to poly it as well before I attach it to the book case. I'm in a small 1 bedroom apt. And I can only stain and poly on my balcony. And it would just be easier if I could do it separately, and secure them later. My backing has some bow in it (maybe 1 - 1.5 inch convex / the 4 feet in height ( if that makes sense)). If I poly both sides, then nail it down to the case, will the poly crack as it is straightened out?