Yup- I've seen that a lot of people veneer after the box is built. Just speaking from my experience. Your pre-laminated MDF is how I'd feel best doing it. On furniture, I usually make up all the panels oversize, then cut and make joints. Never built speakers though- I get the feeling that some...
Putting a finish on will slow the transfer of moisture in and out, but won't block it. Key is to finish all sides- especially large flat one in opposition. Otherwise you invite even cupping and warping instead of just overall expansion. Most veneer furniture is veneered on both sides of large...
I hope he didn't glue to the bed liner! ;-) Raw MDF in a flexy won't cause a problem for two reasons- 1) All MDF- all expands/contracts at the same rate. 2) Compliant joints- unless the holes are drilled REALLY close, you have some slop. Here is a basic article-...
Be a careful gluing wide expanses of solid woods to engineered substrates. The solid wood will move as the humidity changes, sometimes quite a lot (varys by species as well as cut), while the MDF or plywood or chipboard will move at a different rate (usually much lower). For instance in a...