RVing - Importing & Exporting

Called Canadian Registrar of Imported Vehicles (RIV), and asked them the following question:

I'm a Canadian living in the U.S. I'm considering buying a Canadian RV and bringing it here while my partner's immigration goes through, then moving back to Canada with it. How long could I have it abroad before I'd have to register it as an export, and what would be involved?

I was told that I would have to export it as soon as I took it out of the country, and then still have to pay to enroll it in the import program and do the associated inspections when I return, even though it's Canadian-made. They recommended I just wait until I move back to Canada and purchase the RV then.

I suspected this might be the case, for the trouble involved, not to mention the money. Other temporary living arrangements are obviously in order.

Their recorded message gives the following numbers for more information when calling from outside Canada:

(204) 983-3500 CBSA
(613) 998-8616 Transportation Canada

Next question: are there camper shell requirements? I called twice because the first gentleman seemed unsure about what a camper shell is. (There is probably another term for it in Canada, but I don't know what that would be.)

None according to Pierre at RIV, 2/9/07 1:42 p.m. PST.
No restrictions according to Mu at RIV, 2/9/07, 2:00 p.m. - just need bill of sale and title.