I've done it twice now, most recently our new motor home last fall. In both cases the selling dealer gave me the certificates of origin, required to register a brand new vehicle. If used, all you'll need is the title, signed over to you. In both cases we had to pay the sales taxes here in WI to register the new vehicles, something we had anticipated both times and we had checks from the dealer for the proper amount to do just that. Both times were relatively painless.
The first time the dealer delivered the new rig to us. In the second we had plates from our trade in to transfer to the new motor home. If you are doing the transporting from dealer to home you may need to get a temporary tag, depending on the state in which you are buying it, to get you home. In others just having a copy of the purchase order, in case you are stopped, will suffice. You'll need to do some homework to determine what you will need in that regard.
Bottom line, it was no big deal. Just had to spend a little time at the local DMV office to get it registered once we got it home.
Jay & Peggy Monroe with Dolly
Can't take it with you - don't plan on leaving any behind
2016 Newmar London Aire 4553, Spartan chassis
Wrangler Unlimited toad