Every vehicle (campers included) that we have ever purchased or
sold between private parties, we've simply taken our plates off, signed over title, filled out our Colorado state bill of sale (found in DMV online documents) and watched the car drive off or driven our new buy home. No in transit, etc. Most recently my husband drove out to Kentucky to pick up our new to us
Scamp 16, which was registered in South Dakota and whose owner resided at least part time in Ohio. We also took along a South Dakota bill of sale (again printed off of the SD DMV website) so that the sale would match the registration and title when we brought it to the Colorado DMV. We had zero issues, in transport or in titling and registering it to our names. But EVERY STATE IS DIFFERENT. I would suggest you really do your homework.
On another note, our music teacher recently sold his car to a private party and forgot to take the plates off. This week he received a call from another persons insurance, because the car, with his plates, had been involved in a hit and run, only someone was able to write down the plate. The person he sold it to didn't bother to go register or title the car in his name, and now our music teacher is fighting to clear his name, even though he has copies of a bill of sale and signed title.
We always remove our plate and call to let the DMV know we sold it. A refund isn't offered, and I don't know if that is required in Colorado, but it makes me feel better.