I wouldn't worry too much about it, if it were me. Put the food in just before you go, and let it work like an ordinary cooler. The thermal mass of the air in the fridge is fairly low; the food you put in will warm it up somewhat, and should keep it from a hard freeze. (This is doubly true if you're talking about the motorhome rather than the trailer—presumably you'd have the interior well above freezing not too long after starting out for your own comfort.)
Depending on the design of the fridge, it might have more trouble with the freezer not staying cold enough. On some designs, at least on typical older ones, there's only a thermostat in the fridge, and some sort of a scheme to alter the relative cooling of the fridge and the freezer by moving a flap between them or something. If the environment is around the fridge set temperature, the compressor never runs and the freezer never gets cooled to its proper temperature. At least some modern fridges have separate thermostats and some means of cooling the two compartments more or less independently.
