My 3 season room [3sr] has 2 exposed walls and 2 walls connected to the house. Surrounding the 3sr is my patio with sand and 18" x 18" x 1 1/2" blocks. After rains the sand has been draining back under the 3sr. I know i need to fix the slope of the sand to flow away from the house, but below the 3sr is a 1.5' to 2.5' hole below grade. I want to fill it, but a friend warned me not to fill it & close it off completely for fear of trapping moisture below the 3sr. Can i fill up the hole below the 3sr? Should i staple a moiture barrier to the bottom joists of the 3sr? Any other words of wisdom?