Unfortunately, even assuming the insurance obstacles can be overcome, there is a fairly large can of worms just waiting to be opened. Maybe you're going down the road and something (anything... and there is a LONG list of possibilities) breaks. His memory is that whatever it is was working last time he drove. You could EASILY wind up in a less than pleasant relationship with your neighbor... and his family. I'm really sorry to have to say this. It's really sad. But this is, more likely than not, the reality.
Edit: I'm assuming he won't be going with you on these drives because, if he's having trouble with the clothing, he probably isn't much more comfortable being in the rig. If he goes with you, and he's of sound mind (yep, another can of worms), maybe that somewhat tempers what I said previously. It's sad. I know. And I feel for him... and you. You're trying to be a good guy. But this is, these days, more difficult than just helping a neighbor.
