I used to use an ammo can long long ago. Here is one of the larger issues I had with it. It got HOT in the sun. For BP engines, getting them too hot can cause a significant higher cato rate. Even worse, engines that have gotten too hot will retain that damage so they are just as likely to fail later under normal temperatures.
So, I switched to using simpler things like cardboard boxes, which do not get as hot in sunlight. Same goes for car trunks, or cars, just do not leave engines in cars/vehicles so they can get hot in the summer.
On the flip side, when it is really cold at a launch, do keep them in cars, where it tends to be warmer than outside. Because BP engines also tend to cato more often when they are really cold. So, when you are ready to fly, save loading he engine until last, then get it out, install, put in an ignitor, and fly soon afterwards.
I think the best use of ammo cans would be for those who do not get to store their engines inside an air-conditioned house. If you have to store engine in a garage (a garage that never gets hot, but does get damp), or a damp basement, ammo cans would be a great idea. I myself always keep my engines stored inside where it is air conditioned. I have some old engines (from 1970s and 80s) that I know have been stored well, never overheated in the sun, never allowed to get damp, that I expect would work reliably. Then I have others that I do not know their storage history, that I would never put into a good model because of the cato risk.
OK, here is one other good use for n ammo can, even inside of an air conditioned house. For storing composite engines indoors. Humidity can get absorbed into the propellant. The worse cases I have seen this have been some reload packs that I had opened, bun not flown for 2-3 years. Over time, the humidity caused the propellant grains to swell. To the extent that a C slot in a reload grain was almost completely closed shut except for the innermost part of the slot, the rest of the slot walls touched each other.
- George Gassaway