Underground pvc burrow for bunnies?

I'm going for as low maintenance as possible with my rabbits. This is the first year I've had rabbits and I've heard horror stories about rabbits getting too hot and kicking the bucket before harvest time. So, as summer approaches, I'm trying to find ways to keep them cool so they don't croak. They're currently housed in a shed with an open window that sits below several shade trees. But, summers get into the upper 90s here. I'm not a fan of the idea of lugging gallons of frozen water every day or draining electricity with an air conditioner or fan.

So here's my idea: I was thinking I'd attach a currogated pvc drain pipe to the side of the shed and dig a trench underground with several forks in the pipe for mini burrows. I might even terminate the pipe with open dirt since bunnies don't seem interested in burrowing out of ground (just in). Then they can extend the burrows as they please. After laying the pipe, I'd backfill and the buns can move downward when things get too hot. When it's time for harvest (or other such maintenance), I can attach a one-way door to the burrow's opening.

Thoughts? I'm not engineer, but it seems like an effective solution (albeit labor intensive).

If opposed to the idea, any other low-maintenance ideas?

I'm worried the buns will gnaw the PVC.  What about metal or ceramic pipe instead?

Good point.

Might try sticking a peice of pvc pipe in a cage to see what happens.

Good Idea actually to keep it cold BUT.

Domesticated Bunnies behave more like Hares and scratch not even a kind of recess in the dirt or "Nests" for good cooling ground contact.
(I had during my childhood in Germany around 30-80 each season to finance an excessive Discotheque life and impress the Village beauties, with a free drink and cuddly bunnies)

Wild Rabbits are quite good architects when it comes to air exchange, nesting chambers and how to escape predators.
Above that they know pretty good where to dig their holes that they not getting flooded in adverse weather and how to implement levels as water barrier.

As above mentioned I would really try to make a small scale test of a couple of feet, but in my opinion a slightly elevated house where they can go in and hide under will be more appreciated.
I made these shelters from old tree logs about 8 inches diameter (They are keeping the heat well out if shaded) and wooden planks as floor. Entry (min 2 as they love the escape option) in ground level and holes to get above.

Currently trying to get some prices on 6,8,10 and 12 inch pipe. Schedule 40 and concrete.

How big should the entrance to the burrow be?

How deep do I need to go to keep the burrow at an ambient temperature? I know this info is somewhere on the web.

This is for does, but similar ideas should work for fryers.

Yes, YOU have to account for airflow and drainage.  

Standard 5-gallon pails made by United States Plastic Corporation are 14.5 inches high, 11.91 inches in diameter at the top and 10.33 inches in diameter at the bottom. The buckets are slightly tapered for ease of stacking and separat

14.5 inches high. That’s the info I am looking for.

Spoke with a sales rep from Mission Clay in Oakland, CA. He is interested in alternative uses for clay pipe. Someone made a wine storage container out of a huge peice of their pipe and put it in The ground. They have factory seconds that I can look at.

Oakland is about a 1 hour drive from where I am.