Payment of new Camper ordered

I put $5,000 down. A month or so later my dealer called on a Sunday afternoon asking or another $20k- I politely declined. I went to my PDI and paper signing with a cashiers check.

However, I have heard of the situation where high volume dealers do want payment ahead of time. In each case, nothing bad has happened- just seems weird to me. I'm not sure that I would be comfortable with it.