The only two products I ever saw that actually prevented rust in MI were cosmoline and nuxudol.
They both come in a thinner version for cavity coverage and a thicker version for the outsides. Since cosmoline was invented about the time the bow and arrow came off the top secret list, I believe nuxudol is a straight up copy of it. It comes in clean and black...just like cosmoline.
Both of these are long term products. By long term I mean the army sells surplus guns through a special program and these have sat in storage for decades and they have zero rust. But on a car every 5 years would still be overkill.
Use the thinner stuff for inside the frame and inside the doors. The thicker stuff on the outside of the frame, axles, and all other metal parts. I like the clear, that way I can see if a problem is starting. The black looks great but you could get rust behind it and not see it until it starts to the bubble stage.