The 3M paint protector film might be a good choice. Haven't used it though.

The last 240 I had, I had the underbody "rhino-lined". I ended up taking the car back a few months later and having them do a smooth finish on the rocker panels. The car was dark blue and I found they had one almost identical, went with one just a bit darker though, to make it look as if it was supposed to be there.

My brother has had his 196? Toyota done as well. He went on up the car though. Had the whole bottom half done & it's now a two tone car. Looks good though.

I no longer have to worry with snow and road salts, so I'm no real help. I am having my 744 project car's underbody rhino'd though.