I'll add some of my findings specific to tires used in a tandem axle trailer tire setting. These findings may apply to a motorhome also.
All trailer tire brands are not created equal; some brands get weather-checking cracks at 4 to 5 years, while others have been 10 years and not one crack. Amazing! These tires were not covered, and the on the axles operating. I had a friend with General ST trailer tires that were so old they did not have a normal date code on them. They were made in the USA, which was a dead giveaway of how old they are. I told him, you are on borrowed time, and one lucky guy, change them all. He does short trips and got lucky. He has a year 2001 camper built in late year 2000, about the time DOT date codes started changing to the current format. It was now about 6 - 7 years ago when he changed them. I saw those General trailer tires and could not believe how good a 13 to 15-year-old trailer tire could be. I would never trust them that old.
I used to have Maxxis ST trailer tires on my camper when new in 2003. The tires were 5 years old and had the start of heavy weather checking in the treads and side walls. I changed them out due the age, never had a failure, but I for sure had the cracks. Both my friends 2001 camper with the General tires and mine are in the same state of Ohio and had been uncovered. The rubber compounds are obviously different.
I have a full timer friend who I do some service work for them on their 2005 camper. They winter in AZ or TX. Their spare tire had an all black with white lettering on it tire cover, they had the spare blow out on the camper in AZ one winter parked in the campground. The tire was old, 10 years plus old and it was a Mission brand. The Mission ST tires had their issue even in the running conditions, but this is the first one I have seen explode on a covered spare tire parked in the campground. Age, a black cover and heat did not seem to help this tire. And the black tire cover helped hold the heat in even more.
I fully agree, a working tire has a better chance of surviving do to the tire rolling as was stated. But black things sitting still in the high heat, soak up heat badly and fast. Heat is a known breakdown factor of rubber compounds. Camper folks who live in areas of not as intense heat, may fair better then those in high heat, high sun states. The amount of sun and heat, or lack of, are a big factor in what may work for some, but not everyone just due to where they camp, how heavily loaded the tires are and the long distances they travel in the high heat.
Once I became better educated on tire failures, tire capacites needed for tandem axles, heat and tire age, I started using white tire covers when the camper or flat bed trailer is stored outside. Why, less heat plain and simple and heat has been proven to damage tires as time goes on. As to the brand of cover, I used the Adco covers, but I also treated them with 303 Aerospace UV protectant, and that UV treatment really help add a few more years to the cover not disintegrating.
Since our forum spans the entire US, and we all have different brands of tires, stored in different conditions, towed under different weights and distances, what worked for some for 30 years and never had an issue, may not be true for everyone.
Tire age, to the original poster, if you are on 7 years on your motorhome with LT tires, not sure what states you camp in, how much reserve load capacity is on your tires, the pressure you run them at, or the distances you travel, but consider getting new tires, soon. Your good luck may not last much longer.
Hope this helps,
John
2005 Ford F350 Super Duty, 4x4; 6.8L V10 with 4.10 RA, 21,000 GCWR, 11,000 GVWR, upgraded 2 1/2" Towbeast Receiver. Hitched with a 1,700# Reese HP WD, HP Dual Cam to a 2004 Sunline Solaris T310R travel trailer.
