For Alaskans going S... is snowbirding essential travel?

As Alaska is your declared home I would think your 5th wheel in the lower 48 is non essential travel. Just my opinion as I understand the current Canadian rules. I would suggest you call the Canadian border crossing you plan on using and ask the "officials". I would also get their name , badge # and the date / time of the conversation as a reference should they say "come on down".
Safe travels.