I used to live in Iowa were the humidity can be an issue. I didn't really worry about powder and primers going bad, cause i didn't stock up as much and cause I was single and the stuff didn't sit on the shelf long. Now I live in Montana and the humidity is low, but I stock more and it sits longer (I got married, but she does like to shoot).

As far as a portable bench. Make sure it is solid, sturdy, etc. Vibrations, giggling, shaking are an agrivation and detremental to accuracy.