Im guessing a single RHP or a single Flexwatt isnt going to be enough to keep the temps up in a 48 x 24 x 12 enclosure. My house ambient temp is around 75 right now, but it will drop even lower as winter comes.
I use a single (properly sized) RHP in my pvc cages and they do a fantastic job. My house temp is usually 74 and I have no trouble maintaining temps for my IJ's, Corn and BRB Boaphile cages.