Hmm..what I don't understand is...I see SO many of these on Ebay..Craigslist and several other sites...I have even seen 3 that are listed as trailers for sale.Does Coke fly a lawyer all over to put a stop to them selling them..? I mean you own the cooler outright don't you.? Cant you just say in your ad.." Can be used as a cooler..if modified" ? Moondawg..how do you make one into a couch or chair.? Complicated..?
There are some laws about trademarks and if you don't defend your trademark for unauthorized use, you can lose the right to prevent its use. Its not 100%, its reasonable effort. They dont have to chase every ebay sale. If you put it on your website and profit, you may hit the radar. (You may not) The guy I met said he put an ad in the national coke collectors magazine at the time. Coke and Disney are both known for aggressively defending their trademark.
Also, they don't have to fly anywhere, there's usually a local attorney that they can farm the local work to if they see it.
As far as how can the prevent the secondary use, they really can't. Go ahead and start a website, advertise them for sale, and hire an attorney and you will likely win. He got his letter in the 1980's or 1990's, I'm sure it was cheaper then to fight it, the question is... Can you defend yourself in a lawsuit against a billion dollar company with unlimited resources that doesn't want you to do something? I know I couldn't afford $500,000 in legal fees to sell a $2000 couch! Bully, but that's how it is.
