What a hassle.
I'm sorry to hear about your husband and sorry you have to deal with this on your own.
I think you're smart to stand firm on this. In my experience, people who are this difficult to deal with on the simple things (like doing the transaction midweek while the banks are open) will continue to be a hassle after the sale.
I've sold many vehicles to private parties, but selling out last RV was the hardest. People are just so picky.
It's a red hot market right now though, so I think you can stand your ground and tell him you're OK with having this deal fall through. You've done all you can.