So this year we decided to purchase an 18' Ultra Frame, but we got everything late in the season, and being in NY we decided to wait until next spring to put it up. This gives me more time to prep the area. From the pics, you can see I have some rocks to move, but if I plan on putting down a couple of inches of sand and the insulation board, how anal do I really need to get with removing the rocks? Can I just get the major larger rocks and get away with leaving the smaller pebbles and rocks?