You shouldn't have to strip your trailer, it didn't have clearcoat in '55. That's a big plus. If you want to polish your trailer be advised it is a lot of work initially and annually to keep the finish looking good. It is a lifetime commitment... and worth every second spent on it.
Go to www.perfectpolish.com
for all the information you will ever need. Also Shirley Manning has an outstanding website at http://globetrotter64.home.att.net/
They give an in-depth blow by blow on how to polish a trailer.
You can get there by clicking on the above link or on the perfectpolish home page click on Misc info then on Airstream Polishing Project.
I polished my '78 31' Excella. You can see it on my photos on this website. Just click on my username.