I would suggest the reusable Pelican Dessicant pack. Relatively cheap and reusable. Kinda handy to see if you happen to have a leak in an ammo can. with a yearly inspection you can see the indicator turn to whatever color indicates a need for recharge. (250 in the oven for 2 hours)
I also have an undisclosed amount of .50 cal boxes with already loaded mags for various Bug Out Weapons like the AR, Saiga, AR-7, and 10/22's.
just something to think about. The boxes of already loaded mags are the boxes that I would grab first. Boxes of "various ammo" or boxed up extra ammo would be lower on the "SHTF, load up the bug out trailer" list of goods.