I am in the process of replacing the tires on my dual axle, 21 foot, hunting camper before its voyage next week to deer camp. It does have ST205/75R14 Goodyear Marathons on it, the tires that were on it when we bought it years ago. We bought the camper on June 3, 2015, so I know the tires are over 3 years old or older. It is a 2004 camper so I don't have a clue how many times the original owners changed out the tires. I looked at the tires the other day and the tread is starting to separate and is cracked.
I learned a lesson back about 4 years ago about old camper tires. I was towing our old single axle camper back from deer camp in the spring when the tire on the left side exploded. I was on the interstate probably cruising a little more than I should have been. That tire torn up all kinds of sheet metal around the fender well. I limped a mile or so to an exit and got off there at a safe location. I put the spare tire on and limped on home hoping the spare would hold up. Truth be know I believe the spare tire was actually a car tire.
The tires I am looking at are made by Taskmaster Tire, (Contender TTT868). I don't know if they are worth a dime, but if they will last this deer season, next year I might take a look at a better tire. I know one thing they will be in much better condition than the Goodyear Marathons that are dry rotted.
What about Kenda Load Star trailer tires, you guys ever ran any of them. Northern Tool Sells them. Not sure how those would do on a camper?
Ok one last word and you guys can flame and fuss

at me all you want because I know I am running on borrowed time with my 1999 Smith, 4 x 8 utility trailer. It has the 2 original tires on it that came on it in 1999.....

Trailer weighs about 550 pounds empty if I remember correctly.
I mainly haul my riding mower and ATV on it. Oh year its the little trailer you have seen in my wood cutting adventure pictures, its hauled some pretty good loads of wood mostly off road though.
I am going to replace those tires soon, before I have a major failure.