I agree, lettuce will do much better inside in a bubbler system using additional
lights if you dont have a window near by. You can either drill holes in the lid of a tote or drill holes in a sheet of styrofoam and float the lettuce, both work great. All this type of system will require is an aquarium air
pump and some air stones.
My temp's got into the high 90's and low 100's last summer and 2 of my three systems did great with it. The outside bubbler got too hot even with a homemade chiller to cool the nutes. The NFT continous flow system did good and would have done better if I buried the nutes. I just added frozen 2 liter bottles when it got that hot. The system that did the best was the 1/2 55 gallon barrels with pea gravel on a flood and drain system. Again i should have buried the nutes, but I was learning as I was going and the frozen 2 liters did the job as well as increasing the time and intervels of flow till fair week. Someday I will have my greenhouse with some climate control.....