I have an idea for winterizing in ground trees here in Canada I wanted to get everyone's opinions on it.

I will construct a hoop house using steel pipes and coverign with 8 mil poly.  I will put roll up vents on this as well so in early spring and fall I can extend the season on them as well.  When they go dormant I will then put a layer of foam insulation inside the hoophouse all around the roof and walls then a layer of foil insulation on top of that as well.  I would then put another layer of foil insulation on the outside as well followed by a tarp.  This would be all I would do to protect them, I wouldn't wrap them or stuff them with leaves etc, my thought is that there will be roughly 15-20 r value on them depending on the insulation used so I would think this is sufficient to have them survive the winter unharmed.  Of course there would be traps and bait for rodents and mothballs.

Any comments, suggestions experiences are welcomed and encouraged, the only thing is I don't have electrical outlets inside it, although I think I could run a line from a previously existing outdoor outlet I use in the summer for the pond if I just wanted to run a couple bulbs for heat, but I would prefer not to.

Sounds good to me.
Running a line will be good as insurance turned ON only when required.

Chivas ,
Consider what you will do if you get so much snow that it requires you to remove some from the sides so that the load on top of the plastic doesn't collapse the bows. The plastic won't fail ,the bows will with too much heavy wet snow.
If you can run a snowthrower or plow along the side of the tunnel it will allow the snow on top to have a place to slide off.
The top surface needs to be plastic or something slick so the snow will easily slide of or can be pulled off. 

Man; what we north fig nut people manage to go/think through...

Last year I did build an "A" frame structure with wood/plastic on top
of some of my (potted) now inground figs..
Watch for them strong winds!

Yes, the base/root did survive this 2011/2012 winter.
But but but, they did much better with our 2010/ 2011 winter;
not even any any tip damage (with zero/nada protection)...

Go FIGure?

Weather happenings are not predicable.

Did the top growth die down and only the roots survived?

per haps a small ceramic heater you could turn on when needed .

   Chivas...about 3 or 4 weeks ago we went through a pretty severe arctic blast (severe for New Jersey).It only lasted 3 days (first day= 9* F, second day 8*F, third day 7*F), not counting the wind chill factor.   Weathermen said it was the coldest 3 days in the last 17 years. (long before I started with figs)
   I always tripple wrap my trees(burlap, weed cloth, plastic tarp).  I have never lost a tree from winter damage yet(been doing figs for almost 7 years now), but this year I have lost at least 6 of the younger trees so far.  Had to unwrap a couple the other day because we had a fence installed on the property,
and they were too close to the fence line.  The branches crumpled in my hands like straw.  What a heartbreak.
   Said all that, to say this...whatever you have to do to protect the trees go ahead and do it.  The idea you propose sounds like it will give you the thermal barrier that you need.  My only concern is, how many trees do you have to protect like that ? (I have 16 in my back yard).  Sounds like a whole lot of time and material involved per tree.  But when you live in colder climates, you have to do what you have to do.  I wish you the best of luck.

I never did this and the reason was because I was worried about heat build up, a person in my town does it for their figs but uses black fabric to shield them from heating up too much and every winter they survive, single trunk trees.  

I did something different for 4 trees this year, next year will be 9 I think, I put burlap around them after I tied them up and then bubble insulation, then I put a wire cage around leaving minimum 6 inches around open, staked it to the ground, next I put a tarp around the cage.  I filled in the space with cellulose insulation up to the top and then I put the bucket on top.  

I check last week one of the trees and the very top buds were still alive and the wood was green underneath.  we got down to - 18 celcius a couple times this year so I am hoping they are alive and nothing is molding.  I will probably remove just the cellulose insulation next week after the system moves through.

You might want to look into Googling a "rocket stove" for greenhouse heat.
Youtube has some great videos on what it is, and how they're DIY made.
Most efficient heating method for greenhouses, sheds, and even dwellings!
Uses 1/4 the normal amount of wood for burning, uses an  inverted 55 gallon metal drum,
recycles the fire's smoke until it's used up, and only co2 and steam are the only by-products left,
and they can be vented outside, through underground pipes,
which creates an underground radiant heat bank under your greenhouse. DIY Simple to make, and use!
Pretty interesting idea, some very good experiments on heating.  check it out!

Thank you for bringing this up Dan, I was looking at those and wondering if I should do this for the figs in the spring as well so I don't have to drag them in and out but I could protect them from frost, I think I could rig this up pretty well.