What kind is it? Blue and wood or stainless and synthetic?
As long as you don't put it in the case wet, you will be fine. Just clean it good as soon as you can. Wipe it down good when you get back to the truck and don't put it in the case.
All I ever do is wipe with something simple, like Rem Oil. The main thing is don't put them away wet. Don't put them in a wet or humid case and don't let them go through a lot of extreme temperature changes without taking them out, drying and wiping with oil. Temperature changes create condensation and leads to rust.
If you want to paint the rifle, that's a different thing.
At the end of each season, I disassemble and clean all my rifles and shotguns, after a good cleaning of the gun, I wipe a coat of corrosion block over every metal surface. This stuff is pretty badass, I've hunted in the rain a few time this season with blued rifles, and after being in the rain, all I do is wipe them down with a dry towel and let air dry before putting away, no rust at all.
Hunt with it and clean it at the end of the season. If you get rained on wipe it down with a little oil. Some of my rifles are $3k and I bought them to use. I take care of my stuff probably better than most but a rifle is a tool made to be used.