Here's a thought that might be helpful. The transformer causing high frequency tripping the GFCI. I've had digital 600 watt and 1000 watt hps ballasts, especially Galaxy/lumitek, wreck havoc with GFCI, either they trip right away or work for awhile then self destruct never to work again. They emit a super high frequency that you can hear vs regular core/coil ballasts. Have also had bulbs cause the same issues. Move the ballast/hood as far away as possible and they would no longer trip, not always feasible with extension cords that I won't run more than 1 light on, so not a good solution. Just a thought that may help, if I made that confusing enough