Can't help with your insurance question , but there is information that you should have with regard to being a Canadian full time RV'er and travel in the USA.
Maintaining a Closer Connection to Canada, is very important, and depending on the questions asked by the US Customs on entering the USA you could be denied entry.
The Canadian Snowbird Association, has information pertaining to this problem on their web site.
www.snowbirds.org
in particular information on the IRS form 8840. Check in the heading bar under Tax Forms.