i was wondering if anyone had advice or opinions on longterm storage of modern weapons.
such as
bolt cocked or dropped on empty chamber?
oiled, cosmolined or dry?
silica gel type dessicants?
kind of case or cabinet?

Greasegun, plastic bag, nylon ties, steel, airtight 120mm shell container. Store with all springs in relaxed state. Don't draw a map, but don't forget where you buried it.

The above suggestions are excellent, but I think if you are serious about longterm storage, either find a friend who has one, or buy a Foodsaver vacuum sealer for $150.  

They have 11 inch wide bags which you can make as long as you want, since you seal both ends.

Just grease it up, pad any sharp edges, and vacuum seal that baby.

A Foodsaver is great for sealing mags and ammo for longterm storage too.

ED_P, awesome suggestion.  My wife has one of those things. I'd never thought of that.  Excellent, thanks.