I think one thing to keep in mind in these Montana licensing discussions is we should be talking about two different scenarios. The first is the sales tax on the coach. As has been stated by others, and I agree, if you can meet all of the stipulations to avoid being taxed by the state you reside in that's one thing.
The other aspect is the yearly licensing fees. I have lived in CA, ID and NV and they're all different, but for this example I'll use NV.
My yearly REGISTRATION fee is minimal, however my yearly GOVERNMENT SERVICES TAX is based on the value of my coach and is substantial. When I first moved here in 2010 that portion was over $3,000. Last year it was ~$2,200.
Where people get themselves in trouble is once they have legally avoided the sales tax through a Montana LLC, they continue to renew that license registration year after year while the coach is parked at their home. While they may have legally avoided the SALES tax, they are now guilty of GOVERNMENT SERVICES TAX evasion. And yes, I said evasion, which is illegal.
There are other states that also tax a coach based on its value for yearly registration, which may not be call a government services tax, but amounts to the same thing. I believe they are the ones getting caught, and then upon full investigation are found to be guilty of at least yearly tax evasion, and possibly sales tax evasion if they didn't do it properly.