Sean,
I live in CO and also deal with a cold winter. Your biggest challenge is going to be in keeping the floor warm. The ambient and basking temps can be perfect but the floor can be so cool that it causes problems. I had a radiant heat system built in to the ground under the floor in my barn. It's worked really well and allows me to control substrate temps. It's also inexpensive to run in the winter. Here are a few pics:
This is the boiler. It heats 2,000 sq of space and is overkill for your application. You can go much smaller:

Here's the enclosure. There's no cement slab. I have foundation footers that go down about 8 ft. Way below the frost line. Radiant heat pipes are buried 4 feet undergound allowing me to control the substrate temp. Chicken wire covers the pipes so the lizards can not dig into the pipes. The other great thing is the fact that I can soak the substrate and drainage is not an issue. Water drains through the ground as it would outside.
A few years ago I missed a clutch of lace monitor eggs that had been buried in the substrate. After 300 days they actually hatched in the enclosure. I was very surprised to see hatchling monitos running around.


I don't keep Cyclura today. Here's the last pair that I kept about 12 - 15 years ago:
