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The pealing clear coat is common to practically all trailers that are clear coated (late 60's to present). The older the trailer is, or the more time it has spent parked out under the sun, the more likely the clear coat is to be damaged. This is often refered to as "male pattern baldness," since the damage is more evident on the more horizontal (upper) surfaces, and is less evident on the vertical surfaces. On my '73 trailer the clear coat on the roof was practically all gone, but the coating on the sides still required gnarly chemicals to remove.
There are three options for dealing with the clear coat (besides just leaving it alone and forgetting about it):
1) Remove it all so that at least the appearance is uniform, leaving it to develop an oxidized patina.
2) Remove it all and then polish your trailer. Professionals usually charge over $100/ft of trailer body for this service, as it is very labor intensive. You can also do it yourself if you have a few hundred hours to burn.
3) Have the clear coat completely removed, and have it recaoted. This is relatively rarely done. I have only heard of one "reputable" person who provides this service on the Forums, and last rumor was that he was retiring and passing the mantel to someone else. I have never seen any estimates for cost, but I would expect that it is similar to the cost of polishing above, as the operation is similarly labor intensive.
Personally, I wouldn't let the condition of the clear coat count very strongly in my decision to buy or not to buy.