Find a way to keep the vehicle's interior as well as exterior warm. My car used to have that problem during the winter months when I was in S. Dakota until I cleaned up the garage and park the car inside.
After I installed the engine block heater, things even get much better.
If you have to park the car outside then install a portable ceramic heater in the cabin like my neighbor did and plug it in overnight. "Becareful!" He said: You have to rig it right to prevent a possible creating a fire hazard due to the materials in the cabin and set it on the lowest setting"
I never did see how he did it but at a glance, he has cooking pot on the rear seat, the heater was inside the big pot, the cover was on top of the heater and the electric cord fed through a cracked open window.
Of course, he had all kind of other things on the truck: An engine block heater, a battery blanket and an automatic charger for the batteries.
I do beleive there are other options out there, you'll just have to google it to find out...what will be best for your vehicle parking location. If you decide for a portable heater, choose one that will not require oxygen to burn like the ceramic heater I've mentioned above.
I think the best will be install an engine block heater and plug it in overnight, it only take a few minutes after you have the engine run in the morning to warm up the cabin of your car like I did to all vehicle I own when I was in S. Dakota. Never had any problem in the cabin including keeping my.. behind warm in the morning :)
Ps: He got the ceramic portable heater from K- Mart for about $20..HTH