I've already got the ground heavily mulched so at least I hopefully don't lose half of them like last year but I'd like to be sure to keep as much of the thinner growth as I can so I plan on dropping them to the ground and throwing a bale of straw over them..

I manage to get a Himrod to survive up here well north of duluth. It hasnt produced but I still manage to get about 7 feet of vine growth, even in an exposed site (needs to be moved!) U of minn recommends growing grapes on a removable trellis that can be dropped to the ground so they can be buried as described

Our extreme cold temperature wasn't the abnormal part last year. I think the constant snow/ice last year is what did them in. We never had a complete melt off, just slightly melted ice upon ice.
But I'm mostly worried about the thin growth. We definitely get cold enough to kill off less than pinky size every year. If I can keep it alive I could have grapes next year and be very close to having my T's back at the start of the year on most of them.

I don't mind dealing with mulch, I've decided to kill the grass off in that area anyway so the more mulch the merrier. The tarp is what I was wondering so the vines wouldn't be encased in rotting vegetation, or if it would be bad if they were.The bags of leaves might work.
I'll have to go look at UofMN's page.

Thanks for the ideas.

Just don't put mulch down and then cover with a tarp. Put the tarp down and then cover that with mulch. Sounds backwards but it will prevent rot, like you mentioned, and prevent homing vermin for the winter.

Good point. For some reason the bags of leaves kept the soil at a constant temperature.

Here's a link to a post I made concerning my blackberries that were well preserved with the leaf bags.

I generally don't see vole trails in this part of the yard. Maybe they get enough to eat with the root crops stored in the garden and trees planted around there.