Will this Winter Home work for Sulcata Tortoises

My three sulcata tortoises are to big to winter in the house any more so i plan on houseing them outside this winter. I live in San Antonio Texas so the winters are mild down here. I am planning on houseing them in the dog house that is heated by a Stanfield farrowing heating pad (2foot * 3foot) on a T-stat and 2 heating lamps. What I need to know is if I put a clear plastic cover over the opening will they come in and out as they need to for regulateing there body temp?

I kept them that way for years. You should have no problems.