I'm thinking the safe route is the best. Would you rather spend $100K or so on a new RV or loose your family to a fire, accident or anything else that may be caused by worn parts on an old RV? What is the dollar value of your family? Replace your RV every 4 years would be safest. Really, the logic dictates this course of action.
Inspect your tires, check for irregular wear, cracking and so forth. If you aren't comfortable with your ability to check them, then take them in to be inspected. I won't say don't change your tires because they're old.. but my father is 80 yrs old and I have no intention of swapping him out just because he's been around a long time.