No question, get new tires. I speak from experience.
I have always been very attentive (paranoid) when it comes to the condition of my 5th wheel tires, pressure, tread, age, wear, and etc.
Well, about ten days ago I was returning to my home in Huntington Beach, California from Park City, Utah. It was a great day and all was fine, fine until just East of St. George, Utah I was rudely "awakened" by an earth shattering explosion, yep, blow out. Lucky for me I don't normally drive too fast when towing, I was going about sixty. Also, in my favor was the fact that the blow out occurred at a location that allowed me to just barely get to an off ramp. About two seconds later and I would have been stuck on I-15. A few minuets later and I would have been stranded in "the canyon" where pull outs are few and far between.
I know what you're thinking "where am I going with this?" Here's my point, I was so concerned with my trailer tires that I neglected to monitor my truck tires. Yep, the blow out was on the R/R Truck tire. After I safely pulled to the side and had a minuet to reflect on the situation, it dawned on me, holy cow, those tires are OLD, only 35,000 miles on them, but way too old. The F250 is a 2005 so the tires were probably eight or nine years old.
I do have a TPMS and I was monitoring all along. I never got a pressure or a temperature alert (it was very hot that day). Just POW!
Of course, I took a good long look at my truck tires as I stood in the heat that morning, yes, tiny cracking was evident. So, now I have FIVE new truck tires and I have also ordered a NEW tire (trailer spare was never used, but eight or nine years old) for the spare on my 2005 5th wheel. The other trailer tires are about a year old. I didn't want to take a chance with the spare on either vehicle.
So, the moral is..... it is much easier to take care of tires at home then on the side of the freeway.
Oh, did I mention, get new tires? :S
See you out there,
Robert