Another happy knee replacement person here! We have both had them. It's really commonplace nowadays.
First, don't put off surgery thinking it'll get better. It won't. Do the surgery and your life will be good again. Why suffer when you don't have to?
They'll have you walking steps the first day so RV steps will not be a problem.
Do the physical therapy completely - usually four to six weeks and also at home daily. Push it hard. Yes, it'll hurt. If you don't push it you won't have a complete extension and bend. It's not going to break by working it hard. My doctor explained how they bend it every which way while still in the operating room to make sure it's working properly.
It's now usually an overnight or two nights at the most.
Take the meds and the therapy will be a lot easier.
At 10 weeks we were both playing pickleball (similar to tennis) and hiking. We do one or the other 5x/week. We're 75.
Our new knees feel so much better when we use them as in exercise rather than sitting.
We drove the car at three weeks. Driving an RV I'd recommend at least 8 weeks. Get a nice campsite and relax!
We had a friend that the physical therapist even came to his RV.
RVing is definitely doable after replacements and it'll be much better for you.