Ok I just noticed that like an idiot I didn't address all your questions. Going back a bit - to start off with yes it is a sound standard practice to line crates. If you can assure that the crates will be properly stored then your major concern is just that you maintain a good seal to protect against potential leaks. A framed/glazed WOP that is wrapped and sealed should have adequate protection against off-gassing if they will be exposed to only to normal shipping times. The only thing to really be aware of is that it is by no means unheard of for traveling exhibitions to have venues cancelled which can result in objects being left inside their crates for 3 months or more. That isn't really a great situation (and a good case for the extreme (marvel seal solution).
Nomex - this has tradionally come in two forms the most common is soft, somewhat fuzzy and was traditionally used to cover pads or line cavity packs in both crates and for storage. This version is very porous. There is also a more obscure form which is a crate liner and that looks very much like parchment paper. I frankly don't know how effective a vapor barrier that is.

When it comes to expense, it is worth comparing sources on products like marvelseal. In 2011 I helped a museum re examine their procurement practices. During the process sources for Marvelseal varied from $2.29 per square foot to $ .12 per square foot. Contact me directly if your numbers vary too much from mine.