Hi Clive
I can't help you on the low power towel rail or aier.
However, what I do to dry our towels (as we always seem to use more than anyone else) and the dogs have their own towels too, is put a clothes horse in the awning and place an electric fan heater (on the floor and situated not too close, obviously. Even running at 1KW, it does a great job of drying towels. If your awning poles are substantial, you could hang a couple of towels from the horizontal poles and place the fan on the floor near the towels (but not underneath them) and the rising heat will dry them perfectly well. Please remember not to leave the heater unattended as it could become a fire risk. Halogen heaters (try to use the sort that turn off if knocked) in my opinion, do not offer such good drying power as the heat is effected differently.
Hope this helps.
Regards.
Lisa