Hit the surplus store to prevent gun rust
No officer in his/her right mind would allow their duty weapon to collect rust, but that's precisely what many shotguns and rifles do when stored in a duty vehicle for any length of time. While there is no substitute for frequent cleaning, an old military lubricant called LSA might help in between cleanings.
LSA was developed as a cleaner/lubricant for the military in the moist jungles during the Viet Nam war. I have found this lubricant far superior in preventing rust - better than RemOil, Breakfree, and other lubricants currently on the market. LSA can be found at just about any military surplus store. Clean your weapon as you normally would, and apply a liberal coating of LSA to the exterior of your shotgun or rifle.