If you are looking at storing a firearm and never firing it, I would suggest a good microcrystalline wax, such as renaissance wax, which is used by museums for preserving firearms and furniture. I know that the NRA museum uses it on their firearms. I talked with one NRA museum employee who had suggested renaissance wax to preserve firearms for long term storage, so I trust his judgement.
I also found this webpage that goes into more detail about preserving firearms:
http://www.nps.gov/spar/historyculture/guncare.htm
Hope this info helps.