I would sure try it your way first, if overwintering with mulch and plastic film doesn't work for me. The idea of preserving something "wet" sounds to me like encouraging rot.
Leaving them in the ground would be my first choice! Since my usual winter low is only 15-20F, and dialy highs might be I think that a little cover ought to suffice. You go down to -5 to -10, right?
The fact that you get good results at 55-65 F might make taking them inside practical for me, as long as I keep them out of the sunny front room. The shady rooms should stay that cool, and it gives me a reason to keep the night time temps "not below 55" instead of "not below 50".
