Thank you all for the great suggestions and advice. I'll try and respond to all replies.
The items I tried, I had laying around. I didn't need to go out and buy them.
For a few bucks and an easy replacement I would gladly take this route. Unfortunately 2 of the 3 items are not the simple "stretch the collar around the outlet" type. They both require disassembly of the outlet to get them on. Too much effort for me. I don't need them cleaned THAT bad (my wife does though :-) ).
I would not use any abrasive on the actual fiberglass body of the trailer. I know better.
I'll try the Mr. Clean eraser and acetone and see if they work. otherwise. Sorry Wifey....
BTW, I have had good luck cleaned the yellowing off of my fridge cover with a clean, lintless cloth and brake parts cleaner. It takes the very top layer (yellowed) of plastic off. You have to do a small section at a time, and use a clean section of clothe each tiem, but it works well.
Thanks again for all the tips. I'll report back if either Mr. clean or acetone works.