Shovel a hole about 1 foot deep, and 1/2 foot bigger than the enclosure.
Lay down some construction plastic to waterproof the base.
Fill the hole with 10 or 11 bags of rubber mulch, or tires that have been cut up.
Place flat cement blocks on top of the bags of mulch. The solid cement blocks should be about 7 1/2 inches by 15 inches long, and 3 or 4 inches thick. Lay them side by side to create a floating deck.
Place a fiber board on top of the cement to give it stable platform. The generator will be placed on top so it needs to be stable.
Line up cement blocks in two rows of five on either side and on the back of the generator.
Fill in the cracks of the cement block with foam to insulate the enclosure.
Measure and cut three strips of plywood to go over the cement blocks. You can glue foam to the plywood to add insulation.
Line three strips of plywood on both sides and the back. Nail them together with a hammer.