Hi,
I'll let Tireman9 comment on the pictures. That is above me on what could create that type of catastrophic failure.
Can you provide the brand and DOT date codes of the failed tires? While you may have only had them for 2 years, they may be a lot older.
Please confirm the load range of the tire. If you are running 80psi that would correspond to an E load range tire.
I had forgot to ask what year camper you had, but the T264SR was only made from 2004 to 2007. The dry empty brochure weight of those 4 years ranges from 6,130# on a 2007 or 2006 with aluminum siding and no walk on roof to 6,330# on a 2005 or 2004 with aluminum siding and no walk on roof.
There is a shipped weight sticker in the camper, it would be on the door of a kitchen, bath or bedroom closet. But still, in your case unless you have something massively heavy in the camper, you should not be out of tire weight capacity and the extra reserve capacity needed for tandem axle trailers. The camper is not that long either at 27' 7".
Sunline rates the camper at 8,600# which allows 2, 270# of cargo assuming the 6,330# dry weight and puts on ST225/75R15 LR D's on it or 2,540# per tire or 10,160# for all 4 tires.
If you have E load range, it is 2,830# per tire, Or 5,660# per axle and total of all 4 to be 11,320#. And this is only the axle supports. The average loaded TW on a T264SR is 1,000 to 1,200#. Figuring 6,330 dry - 1,200# loaded TW - 11,320 = 3,820# of tire capacity for cargo. If you put that much weight on the axles, the leaf springs would be having issues as they are only rated for 8,600#. Or if you had one side very heavily loaded.
While we do not have actual loaded weights, and unless you have something really heavy in the camper, tire weights are not floating to the top. But should not be lost site of.
While the tires failed at a certain MPH, what is your normal towing speed on the highway?
Do you recall hitting any large potholes or large bumps? At any time since you had these tires, even a year ago etc. The highways can be filled with them.
Hope this helps
John