I also work at staying as fit as possible and applaud you for your efforts. The work is worth it, isn't it?
However, I am 71 and during the past 10 years have had 2 knee replacements, a broken ankle, and a back injury. Sometimes life just throws it at you. I find that my trips have changed from drive/hike to drive/sightsee/stroll, but I am still out there, still enjoying RV travel safely. That's what matters, that we enjoy it and do so safely for ourselves and others.
In addition to your personal trainer program, you might take a look at
http://www.thefitrv.com/, which shows exercises specifically for issues common to RVers.