Remember, in general, RV dealers make car dealers look like choir boys.
By delivery, do you mean deliver the RV to you as in you're not driving there and picking it up?
They have their deposit or earnest money. Reckon, I'd wait until PDI, all repairs, etc are complete (you know since they don't repair sht UNTIL someone buys it, there's a reason for that btw).
Then cut the check, hand them a bag of money or finalize the loan with them, however you're paying for it, and sign any paperwork at that time.
You're doing well by being cautious and I'd continue to do so. I'd also be towing it home myself. Then you can make sure brakes etc work before leaving with it too.
