I guess I'll say it again:
KNOW the law in your state.
COMPLY with the law in your state.
DOCUMENT your compliance with the law.
For example, if you live in California, the law says if you keep it out of state for one year, and can prove that it was never in CA for that calendar year, you can register it in CA without paying any sales or use tax. It really IS just that simple!
"I thought I was being very careful,but when my Montana LLC bought a DP from a dealer in Florida and took it home to Illinois, it took them maybe 14 months to come after me."
"...took it home to Illinois..." It may well be that in Illinois you can NEVER bring it "home"! If so, when you did you gave them the chance to come get the money!
AGAIN:
KNOW the applicable laws.
COMPLY with the applicable laws.
DOCUMENT your compliance with the applicable laws, in whatever way the law requires!
IF, by law, you must leave your new coach outside the borders of your home state forever, that is what you will have to do!
Come to think of it, there is another way to avoid the sales/use tax in SOME states. SOME states exempt in-family transfers from tax. IF YOUR state does, and you have a close relative in a NON-tax state, put the coach in his name, then have him transfer it to you when he gets the title. You will pay no tax!
(yes, I have done something similar. Several times!)