This is nonsense.
I recently imported a Canadian-market truck with a US-made camper titled in one state, purchased from another state, and got it all squared away in 2 easy and short DMV visits plus a trip to my local CARB referee. The 2nd visit was only needed because I needed to see the smog referee, and the trip to the referee was only needed because it was a flatbed conversion and the original smog shop had a (valid) question about the fuel filler conversion done when the original truck bed was removed. If not for that, I could have handled it on my original visit which was a Friday-afternoon walk-in.
For the OP - visit the DMV website, do a search on "out of state import", etc. as appropriate and read the pages that come up. They will refer to you a number of forms. You
could print and pre-fill some of these, but you may be handed blank ones when you get to the DMV anyhow, so it's up to you. The main thing is to look at the forms in advance and be prepared to provide all the necessary information.
For RV's/Campers, depending on the type of construction, one of the big things to make sure is done right is in the "Classification" on the Vehicle Inspection form:
https://www.dmv.ca.gov/portal/uploads/2020/06/reg31.pdf (This is one you CANNOT fill out, but reading it beforehand will help you know what the inspector will be looking for) You'll need to have a DMV rep (or other valid rep like a CHP officer) fill out this form and assign a Body Type code (see page 2). Since I have a flatbed, I could theoretically have been categorized as a commercial vehicle - this would have made me liable for a bunch of extra taxes and changed my obligations with regard to weigh stations, etc., however since my camper is permanently affixed, I got the type "PM" - (Pickup with Camper Mounted), which is a passenger vehicle class. Obviously if I remove the camper and use the vehicle as a flatbed, I'd be obligated to re-title the vehicle, but that's a non-issue for me.
This same form is also how they do the validation of the VIN, Smog labels, safety labels, etc. - it all happens in one quick inspection, IF (and I cannot stress this enough) - the vehicle is
actually legal for import. If the vehicle has all the right FMVSS/CMVSS and EPA or equivalent labels, and you have all the relevant paperwork (title docs, import certificates if coming from outside the US, etc.), this is not hard.
If, however, you are trying to import something that is not actually legal, or is maybe legal but missing documentation, then yes, you're going to have a hard time. While I was waiting on my inspector, the couple ahead of me was trying to get their Louisiana-sourced Hyundai through the process, but it was missing one of the labels, either because it was grey-market, or (more likely) because it was a salvage recovery and the hood had been replaced without the all-important label. They were having a bad day.
Bottom line: Know what you need to know and what documentation you need to have. Make sure you have it before you get to the DMV. Better yet, make sure you have it before you close the deal (make it a condition of the sale). You'll be fine.