Yes, it CAN be done, and it is quite simple:
1. KNOW the laws in both your home state and the state where you plan to make the purchase.
2. COMPLY with the laws in both states. If that means you can never bring your new RV to your home state, so be it, DO NOT DO THAT! If it means that you have to leave it and use it out of state for a certain period of time, DO THAT (BUT, see #3).
3. DOCUMENT your compliance with the laws in both states.
Yes, you CAN save a large amount of money by not paying sales tax, BUT you must OBEY THE LAW!
For instance, California says the vehicle MUST NOT enter CA for one year after the purchase date. If it does, and you get caught, you will have to pay the taxes and penalties. If you comply with the law, and document your compliance, after one year it can be brought into the state and registered without paying the sales or "use" tax.
Good luck.
CM1, USN (RET)
2017 Jayco TT
Daily Driver: '14 Subaru Outback
1998 Dodge QC LWB, Cummins, 5 speed, 4X2
2 Kawasaki Brute Force 750 ATVs.
Pride Raptor 3 wheeled off-road capable mobility scooter
"When seconds count, help is only minutes away!"