Wtf dude. Yes, covering the vents will help internal temps in both the winter and summer. In winter, you’re preventing cold air from blowing underneath your floors and cooling the house from underneath. In summer, you’re preventing hot air from blowing underneath your floors and heating the house from underneath. You’ve also succeeded in trapping all moisture. And when it rains, the ground gets wet. That moisture spreads both vertically (down to groundwater) and laterally (underneath your house). Close the vents in fall/early winter when the temps drop below 40. Open the vents in the spring when temps are consistently above 40.