Seven year old tires on a heavy vehicle where you do not carry a spare (I would never consider changing a tire on my full size diesel pusher even if I DID have a spare and an appropriate jack...) is taking more of a chance than I would take on a trip out of the country.
The only time I delayed replacing tires on an RV was on my travel trailer that got very little use and was always stored inside -- those were 9+ years old and had only about 3000 miles on them. Tread looked perfect, of course. Yes, I had a flat in the middle of a long stretch of freeway. At least I had a spare tire/wheel and the jack on my truck sufficed to allow the repair...but being on the shoulder with semi trucks blasting by at full highway speeds was disconcerting at the least!!
Its your rig, but saving a bit and having the possibility of getting into trouble on the road is not what I would choose.
2007 Tour Master T40C
Acura MDX toad
"It takes a great deal of time to recover from any improvement..."