Hi John. Yes, figs can survive in zone 5 with lots of protection. Here the method that has worked well for the past few Winters.
My in-ground clump is 9 feet long X 3 feet wide.
There are garden posts pounded in the ground, 2-3 feet apart. They are positioned around the perimeter of the 9 x 3 fig clump. They are 5 foot posts, so 1 foot is under the ground and 4 feet are above.
There is a row of 6 foot posts pounded through the middle of the fig clump/bushes the long way about every 2-3 feet. These higher garden posts help to create a peaked roof when a tarp is put over everything in the last step.
(I usually trim the clump to a 3.5 foot height.)
Insert heavy black roofing paper between the posts and the fig trunks.
This creates a rectangle of heat absorbing black paper that also blocks the
wind. From trial and error, I've learned to push 4-5 inches of the black paper flat to the ground to help create a barrier against moles, voles and mice.
Next comes a layer of R-15 aluminum faced bubble wrap insulation. This can be purchased at H.Depot or Lowes. I found some on the Internet, but that was 6 years ago, so prices will have changed. My roll was 50 feet long and 5 feet high.
The bubble insulation is inserted between the black roofing paper and the fig clump/trees. Again, 5-6 inches are pushed flat against the ground, cutting slits to facilitate the bubble insulation being able to be flat on the ground. (critter barrier)
About 1 foot of bubble insulation will be higher than the fig clump/tree.
The interior of the fig clump is loosely filled with DRY, clean straw, leaves or newspapers. If it is damp, then a moldy mess will form.
Once the interior is filled with the straw, then the remaining foot of bubble insulation is folded toward the middle of the fig clump/tree. Cuts are made as needed to help the wrap to fold inward.
An additional 9 foot length of bubble wrap is laid on the top of the fig bush clump. Since some air circulation prevents too much condensation/mold, the top length is placed loosely on top and not weighted down. Insulation is wanted, but not suffocation.
A large plastic tarp is placed over the whole clump and then a second tarp. The bottom edge of the tarp that laps against the ground is weighted down with heavy rocks to keep our strong winds from causing rips.
In March or April, I remove the tarps and the first layer of bubble insulation wrap, from the top of the clump. On sunny days with higher Spring temps, the flaps are opened to let the fig branches start to warm up and breath. The straw is left in place. If a Spring frost is predicted, then the top layer of insulation wrap is put back on for the night and removed in the morning. If it is windy, then the top piece of insulation has to be weighted with a few boards or rocks so it won't blow off.
When temps are getting fairly higher in April-May, the straw is removed and the insulation bubble wrap is pulled out. Only the black roofing paper is left in place.
My clump is planted next to the Southern exposure of my barn. The sun hits the black roofing paper and is absorbed, helping to give the figs a good start. When temps are safely warm, the black roofing paper is removed. After four years, my fig clump has become an aggressive grower, so frequent pinching and occasional major pruning are needed.
I chose Hardy Chicago and Celeste as my in-ground varieties. Of these two. Hardy Chicago wins as the best in-ground variety for my climate. I have found that it has higher productivity when fruiting branches are kept shorter than 3 feet in length. It also does better as a bush/clump. Great tasting fig that ripens even in cooler Fall temps with no splitting.
Important to note that these figs were planted outdoors in the ground after they were 4 years old. A younger plant would most likely suffer or demise from our Winters.
Hope this is helpful. I am sure other materials could be substituted for insulation.
near Buffalo, NY