After 25 years of working in the PNW, being an armorer and range instructor, I basically came down to a simple method I recommend especially for patrol AR15’s in soggy areas:
Breakfree CLP (or just LP) on the outside of the rifle (steel parts like barrel/FSB, etc). It consistently has been shown to protect against rusting in exposure tests done by numerous folks. Failure to use something on the exposed steel parts will quickly lead to rust to some degree, but BF CLP does well if you at least dry the water off and reapply CLP once in a while. It also is OK for a lube, but it will dry off fairly soon, and burns up after a few hours of shooting. Reapplying at a break always improves sluggish guns.
MOBIL1 for the interior parts. Bolt/carrier/locking lugs/trigger components/etc. MOBIL1 just seems to hold up much better than CLP- it does not need to be reapplied halfway thru a range day, it does not seem to dry off in storage or from just being carried. It took me a long time and lots of testing and a letting another major agency try it out first, but I am convinced it is better than CLP for the inner workings. MOBIL1 is not good for the rust protection aspect, so don’t use it on the exterior.
That’s it for lubrication. Simple, cheap, effective. Worked well (for the people who listened) on a fleet of over 100 rifles, including our SWAT rifles which got a lot more use and even more exposure to bad conditions.
For cleaning you can use whatever you want, CLP, Hoppes, MPRO7, etc. Just finish up by drying it completely when clean, then lube with CLP on the exterior and MOBIL1 inside. We used MPRO7 a lot, but I had Hoppes for the diehards as well. Obviously it is an AR- it is more important that it is well lubed than well cleaned.
Do not use shit like froglube, people don’t do it right (I guess) and I dislike telling people their gun won’t function until they remove their “lube” from the gun. Had a few non functional guns from that stuff over the years.
Plenty of other stuff is just fine, maybe even better, it is just overpriced or doesn’t offer enough improvement for the cost. Too often the good lubes fail at rust prevention, and the good rust preventatives are not great lubes or burn off quick.
It is an un-contained system. Don’t over think it.
You could even paint the exterior and just use MOBIL1. Lots of ways to solve the problem.
Added- above advice is specific to AR15’s and similar rifles. I have other recommendations for pistols, other types of rifles etc. (Although it is pretty decent advice on 870P shotguns.)