Hi Frank & Val,
I too will be looking to do similar to you guys when and if I get my house sold but I have done a lot of investigation as to an aussie owning and keeping a motorhome in the USA.
There are many things to consider, including perhaps creating an LLC in Montana to have an address in a state that has some advantages when owning vehicles.
Insurance is doable as far as I have seen with some choice. I would advise that you take existing aussie policy with you to establish your rating 1 status etc.
You can also open a US bank account in Montana. This is one of the options for Montana - Montana RV Registration | MT Registered Agents | Tax-Free Montana LLC : Deer Creek Corporate Services
Doing a google search including LLC and Montana will bring up a few companies that do this kind of thing all the time.
As to choice of motorhome, I can't see any issues with you taking a small class C to Alaska at the right time of year.
If you want to send me a PM, I can leave you my phone number if you want to have a chat about it at all. I live on the Gold Coast.
Hope it all works out for you guys as I can imagine nothing better than touring in an RV around the US of A.