I bought a truck in Virginia and paid 2% sales tax. Two years later, I moved to Vermont that has a 6% sales tax on vehicles and had to pay the prorated difference. While I am happy to buy big items in sales tax free NH, I do tell VT that I shop in NH and online when I file a tax return and they assign a prorated tax to cover it. Your best long term bet is probably to establish residency in a low income tax state and not worry about sales tax as you won't be there much anyway.
2015 F350 XLT PSD CCSB SRW, Andersen Ultimate hitch
'12 Cougar High Country 299RKS, Mor/Ryde Pinbox
1/77 Armor Bn, 5th Mech, I Corps