I have a tent in my garage that had a similar issue. I was using an HPS lamp with a glass cover and was blowing air into the lamp housing with a 4" duct and straight out with more 4" ducting. This keeps as much thermal load of the lamp out as possible. The good news is the temperature at the bottom of the tent was a good 4 to 5f lower in temperature.
So, since the temps outside the tent are averaging 45f this time of year I placed a reservoir outside the tent and used a cheap aquarium pump to send cool water into the tent, through a flood tray and then let gravity send it back to the cool reservoir. A timer controls the pump and it floods and drains several times a day. It is a pain though cause when the weather gets warm I have to shuffle ice out the garage to put in the main reservoir. Had been using plastic jugs with a cap so they can float in the main reservoir and cool the water that way. Between this tent and my my flower room I was always busy ferrying ice out to the grow areas. This is why I ended up ordering a chiller this week. Ultimately the plan is to use RDWC in both rooms. I was trying to get by til April or so when I can grow outside til Fall when cooler weather returns but the weather lately has been unusually warm.
Recently I also built a COB LED light bar for this tent to further reduce the heat load in the grow.
Best Wishes,
D
