Don,
Reflecting coatings will only reduce radiated heat transfer. I doubt that you have much of that type of heat loss under the floor in the winter. It may reduce heat gain in the summer when parked or traveling over asphalt, but I doubt you will be able to detect much of a change. White will work almost as well as metallic.
Since (I understand) you usually have electric hookups in the winter, why not put an electric heating mat under your existing flooring?
Electric Floor Heating MatsThe mats are ~ 1/8" thick and use ~ 12 watts per sq. ft. They won't change the heat loss through the floor (that takes insulation), but they will make your toes smile.
Steve