From experience, if you have cracks in the sidewalls, expecially Marathons, get rid of them ASAP. I had them on my 5er, just sitting over the winter, and didn't even notice the cracks. Tires and tread looked real good. Come spring, there was a piece of the sidewall laying on the ground beside one flat tire, and a bulge where another was getting ready to blow. Replaced with Maxxis as suggested by others on the JOF, and have had no further problems. BTW, I understand that all GY trailer tires are now made in China, and there are many problems, just FYI.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.