We have done similar many times in our TH. Temps even lower than that on a few occasions but daytime temps always returned to 40 degrees or so. We ran our genny quite a bit and it seemed to help warm area under our rig that is open to the elements as well.
We camp in those conditions with FW tanks full and do utilize our grey and black tanks. Obviously, if it didn't get above freezing during most of the daylight hours it would be quite risky, and there is no guarantee your rig won't suffer ill effects from doing so under the conditions you outlined above. Enjoy the race!!!