His cognition is good. He walks with a cane due to hip instability. We have suggested he stop pulling his trailor. We have suggested he down size. We just think he has no business pulling a trailer regardless of the size. My mother has dementia so she is no longer a help. Do we wait for an accident and hope he doesn't hurt himself and his wife or God forbid anyone else?
The more you make it an overt issue, a contentious point, without having proof that he is a danger, the more he will resist any changes or compromises. If I were in your shoes I would make an excuse to get him to drive you around (or enlist another family member, neighbor or friend) to really get an accurate idea.
And most importantly, although I don't spend time studying them, I usually see 2 hands on the wheel, not one on the wheel and another holding a tech device to their ears. Of course people can use ear plug-ins, but they're still not focusing on the primary purpose or driving - to get somewhere, safely.
I can certainly understand your concern; I had that when my father was driving, but I had an interesting experience once. I had hired some young men in the neighborhood to help clean out my sister's house, and they were watching Dad as he maneuvered around in the storage area where I was keeping her things so I could clear the house.
These were young men, some teenagers, and I overheard them commenting on how careful Dad was, one even observing that Dad certainly had a lot of experience managing and hauling trailers. I began to realize that I might have been too worried. Different perspectives.
How far will your father be traveling? Across the US? I'm thinking that another issue perhaps equally if not more important is the issue of traveling through states with high Covid infection rates. Does he usually stay at an RV park, something like the Snowbird parks down South?