Outside Terrarium

The problem:

One of the stipulations for getting our snake was that it stays outside in our shed. It's more like a small barn. I have plenty of power sources and wooden counters, so except for the fact that it's outside, it's a perfect place for terrariums.
The weather in Alabama is fairly mild in the winter. We hit temps below 40 only about 80 days this year. In fact, this last year we had less than 900 hours below 45 degrees. However, I know I need to be prepared and I'm gonna need to be smart for this to work.

Current setup and considerations:

Sunny, our snake, is in a 10 gal aquarium with a UTH. He is 26 inches (66cm) and weighs 76g. Right now the temp in the cage is around 80-86 degrees at the hot spot (using a temp probe), so summer doesn't seem to be too bad of a spot for the terrarium. When winter comes, I'll need to ramp things up to maintain a safe temperature.

My plan and thoughts:

Use insulation foam around the outside of the glass,
Use both a hotspot lamp with the UTH and temp probe to add more heat
(Should I use two probes, one with each heating instrument if I do this?),
AND
Use a plexiglass top with less holes than the current mesh top to hold in more heat.
When temps get into the 30s or a freeze comes, I'll move Sunny into the house in the laundry room (wife has allowed this compromise).

Past successes and failures

I kept two leopard geckos in the shed in a large plywood, home-made container for many years because my son was born and my wife didn't want them around the baby. I solely used heat lamps and no UTH since it was plywood. Unfortunately, a lamp failed while we were out of town and a freeze occurred. Neither geckos survived. Up until that point, they were healthy, and I hadn't even been introduced to temperature probes.

We got Sunny in April, and although temps only got into the 40s the UTH kept the hot spot right where it needed to be at at 82-85 during the day and around 75 at night.

I have time to prepare as the temps around here don't start getting into the 50s until around Sept or Oct., but I wanted to see if anyone had any suggestions prior to crunch time when an actual freeze is on the way. We got Sunny in April, and although temps only got into the 40s the UTH kept the hot spot at 82-85.

Honestly, I have sat on this post for a while because I do not want to be laughed off the forums or harangued because of the situation.