Moishe, I get the feeling it almost depends on the agent you talk to and how the question is stated and perceived. Al I can tell you is what this particular agent told me.
I also was curious about shipping the RV across the border . One transport company guy told me it wasn't allowed.?? even though it seems lots of people have done it.
So, I phoned the Coutts border crossing and talked to the US border agent and she stated that "at this time" , we are still allowed to ship our rvs across the line.
One thing I would recommend is for people to contact Mariposa at KM 21 and if closed to Canadians at least you could get a new tip and stay for another 6 months , ...If you had to...
It would be to late if you were told at the border that you can't cross. However... I find that whole scenario unlikely . Maybe I'm wrong, who knows anymore. We live in interesting times.