Save your money on the cool tubes. Venting is a pain in the ass (moving fixture height with duct work) Too much lumen reduction with anything under 1000w. I didn't know you were in a tent. I would still go 400 dimmable, as the heat with one fixture should be OK, you can move the fixture close at 300w, which will be more effective than a 600 w cool tube at 3' above canopy, which could cause excessive heat, depending on ambient heat.
