Nathan,
Well we have managed to purchase our rig. It is registered temporarily in Ohio where we bought it, or rather our Montana LLC bought it. It is now in process of being registered through our LLC in Montana and we should get all the paperwork and the plates through in a week or so.
Not only did we get a good deal in Ohio, we saved paying any sales tax by using the Montana LLC route. We set up a Montana LLC using New Horizon RV but there are several companies who do the same thing. Since we are not US residents or citizens we have no problems with our state of residence (the UK), we used a UK drivers license plus an International Drivers License, which is needed in the USA and our UK passport number served as equivalent to a US Social Security Number to get temporary registration.
I understand that US citizens can have problems with this route as their "home state" may view the Montana LLC as a tax evasion loophole, but as a non US citizen this does not affect us as we have no residence in the US. Can't see why it should not work for any foreign national. Of course it costs about $850 to set up the company so this has to be offset against any potential sales tax saving.
Insurance costs as far as I can judge are no different between Montana and Texas, the only comparison I made - can't see any other state insurance being much different. For what its worth we went with Progressive but Explorer had a similar deal.
Hope this helps and good luck.
Alan