Exciting eh?
In Corpus Christi which has about the same RH and heat you have I had exactly the same config as you except the lean too was attached to the entire south wall of a garage, painted white for reflection same as your OSB board. Grew the hell outta orchids, ferns, etc. I installed a high speed fan in the ridge of a short wall and on the opposite short wall installed a willy nilly aspen wet pad that worked very well for cooling. I basically laid out a 12' roll of 1X2" hardware cloth on the ground, snipped the wires here and there and bent them in 90* to snag/hold the pad, folded it up to make a 6' pad, wired the sides closed, hung it with a recycle pump, float valve, perf. PVC pipe overhead etc. etc.
Door had a flat panel hinged on the top at the bottom framing kept close with a few magnets at the bottom, sealed with foam tape. Come winter when the temps got up the exhaust fan would kick in, flip the panel open and cool perfectly.
Mark