I like riding at Utah's Sand Hollow State Park during that time of year, but the weather can be hit or miss as to how cold it might get. Fairly good chance of below freezing temps at night. You'll find this area between St George Utah and Zion National Park. Here you have Sand Dune options, or some pretty good rock crawling stuff. Myself I even prefer it if you get a little snow, but that doesn't happen often.
Another option is the Valley of Fire State Park in Nevada. It can get crowded on the weekends during the winter months, but it is generally fairly good weather wise.
Make sure you let us know where you end up and how it went. Sounds like a potentially great adventure.