I used Chassis Saver by Magnet paints.. It is holding up just fine.. at the same time, I used the leftover on my trailer and it STOPPED active rust, with NO pretreatment or cleaning.. (not recommended)
I have some more spots to do, but the ones I did a few months ago don't show any sign of rust starting back up..
as a preventative treatment for a NON-rusted frame/chassis componants, EITHER product will do you just fine.
READ AND FOLLOW THE INSTRUCTIONS on whatever you decide to use.
I used to use POR-15, and it is GREAT..... but.......... I like Chassis Saver better... I have read a LOT of reviews of the two, and it seems that everyone prefers Chassis Saver..
BUT... POR-15 is a wonderful product... they cost about the same.
The reason I switched was really just an accident. I ran out of POR-15 and didn't have time to order any, and noone carries it around here.. mail order only.. there is a local paint supply that carries Chassis Saver, and it came highly recommended by the owner of the paint store... SO... I tried it, and never looked back..
You can't go wrong with either... OR the Wurth product.. all three are VERY similar..