Supplies needed -  
Three - wood pallets (strip the top and bottom (skid) slats from one and reserve )
Nine  -  5/8 in. x 5-1/2 in. x 6 ft. wood fence pickets
Four - concrete blocks for a base
One – ribbed black plastic carpet runner (2 ft. x 6 ft)
One – ¼ in x 4 ft x 6 ft. rubber mat
Four  - bags of rubber tire mulch
Six -  dense fiberglass insulation boards (about 2 in. x 18 in. x 18 in., wrapped double in wood pellet        bags)
Box of ceiling tile staples
Box of 1-1/4 in. exterior Phillips wood screws
Lots of scrap bricks, concrete border, and concrete blocks (counter balance and safety backstop)
3/16 in. nylon cord and a roll of duct tape

Tools needed – 
Electric drill
Staple gun
4 ft long level rule
Saber saw

Instructions  –  
Remove the top and bottom slats from one of the pallets, remove all nails, etc. 
Measure the outside edges of the pallet that you’ll use for the bottom, front to back and side to side.
Align the concrete blocks outside edges to those measurements and level them four ways (side to side, front to back, and to the other three blocks.

Step 1:

Place the bottom pallet on top of the leveled blocks, centered.
Fill in the front three openings between the top slats with the ones removed from the third pallet.  Use the wood screws, and use only one per end.  Turn the remaining pallet on its end, and screw in a slat into the top and bottom to make a box to hold the insulation. 

Attach the pickets to the top pallet using the wood screws – three screws per picket, top, bottom and center.  Make them touch side to side, align the first picket in the center of the pallet, and work toward the outside edges.  The flat bottom will be even with the front edge of the top slat (the end cap you added will extend past the bottom of the picket).  Measure 18 in. from the top end cap, and cut the pickets to that level.  Place the bottom of the top pallet in the first gap between slats of the bottom pallet   Using the nylon cord, tie the top pallet skid  (bottom slat) to the rear of the bottom pallet, using three cords (each side and center, using two loose taut-line hitches.  Adjust the cords so that the top pallet leans forward about 25 degrees. 

Measure the length needed to secure the side and center supports from the top pallet to the bottom pallet, to keep the 25 degree forward lean in place. Cut the remaining pickets to that length, and secure to the runners (three thick upright pieces that the slats are attached to) with three screws in the top and bottom (see illustrations following).

Front view with pickets attached and top trimmed even: