So far, I've had pretty good luck with the VCI bags that Kleenbore makes for pistols and long guns. Strangely, only the handgun bag has a zip loc top, while the end of the long gun bag is open and I just fold it over several times and use a "chip clip" on the end.
You still have to oil the important areas, especially the barrel, chamber, bolt face, etc. but they seem to do a pretty good job, if you aren't constantly taking the gun in and out of the bag.
I've even put one of those dessicant things like Cabela's and Bass Pro sells that look like an aluminum bar of soap with the crystals that change from blue to pink when they need recharging in the bag. These things always seem to turn pink fairly quickly in a safe, but when I put them in one of these bags, it stays blue all the time.