I have considered what you said because:
The majority of the water of the system will constantly be in the tent, where only a minority sits outside the tent..
Buuut.. air is a really good insulator and there's some bubble on the reflectix and it would reflect off the all black pipes and buckets so the light reflection would be nice.
I'm on my first grow and it was almost dying in the beginning cause of heat in the DWC only buckets, but I really like the idea of growing only in water. Seems futuristic (lol) Maybe I will switch to a different system, I like to idea of trying different systems seeing which I prefer most. Progress of my plants coming along in flower right now, I knew theres no way I am doing a DWC only system twice, once was enough.. watering everyday. Now I will see how RDWC is, might draw same conclusion as you in the end lol.