We brought our US flagged boat back to the US, registered it in Florida and paid no sales/use tax, even though it had been registered in NH, which has 0% tax.
When we bought it in FL in 2000 I spoke several times with the director of the Florida sales tax division that handles boats so as to "get it right". He informed me that if we left Florida in 10 days, (or checked into a state registered repair facility and left FL afterwards) and registered it in another state and sent him (the tax department) proof of the boat being out of Florida and of the other state's registration there would be no tax due.
He further explained that if we subsequently brought the boat back into FL after, if I recall correctly, 6 months, we could (should) register it in FL but the fact of having "met the sales tax requirement of another state" (even thought that was 0%) would mean no FL sales tax would be due.
So after 15 years we came back to FL and were not required to pay sales tax, just the normal annual registration fee ($200 or so).
The sales tax director said it was just like the thousands of people who move to Florida and bring their cars - if they come from a no- or low-tax state they do not have to pay the difference in the sales/use tax rate.
Craig Briggs SN68