I really enjoyed installing a ground-to-air heat transfer system (geothermal) under the greenhouse which consists of two 4-in duct fans and 200 ft of Big O tubing buried 4 ft below the greenhouse that acts as a heat storage which helps level out the temperatures and keep it from freezing in the winter at minimal cost.
As we live next to a golf course our worry was damage from stray golf balls. The greenhouse has been hit by golf balls with no damage as the polycarbonate takes the ball hits.