I've gotten a few 80% lowers that are in the white.
After I perform the final machine work, how do I want to finish them?
If I understand correctly, most anodizing companies won't deal with finished lowers that have no markings / serial numbers.

What can I use to put a protective coating on all these bare surfaces?
My biggest concerns, are all those hard to reach nooks and crannies. (inside the take down pin holes, for example)

I used this product from Lauer:
http://www.lauerweaponry.com/index.cfm?fuseaction=category.display&category_ID=929
I found it to be easy to use and got great results.
There was a long cure time though. Fortunately, I had lots of time.
Good luck.