Most of the heated gear you can buy is designed to work on motorbikes or small disposable batteries so I wouldn't see this creating any problems for the 3 wheeler.
I've got some stuff from here on my xmas list
Heated gear.
I went out a few weekends ago and was told the temp was down to -2.5. Even with outer gloves and lining gloves my hands were cold, but the bigger issue for me was my feet. At this temperature all you really need is some trace heat which shouldn't drawn to much from the battery.
