Arrange the frame pieces and hardware on the floor in the approximate location where the bed will rest. Make sure the grooved edges of the rails will be located on the inside bottom of the frame and the finished edges will be facing out. Place the corner brackets and screws at each corner. Set the decking and pedestal parts aside.
Press the corners together, and secure two corner brackets to the inside of each corner with a screwdriver. The side rails will extend beyond the top of the frame to support the headboard once the bed is assembled. Position the frame exactly where the bed will ultimately rest.
Lay the drawers and hardware out in the center of the frame, with the drawers facing out. Insert the spacer boards into the grooves between each drawer. Use the finished spacers along the foot of the bed and the unfinished spacers on the interior. The drawers and spacers will connect to form a pedestal in the correct size and configuration. Turn the exterior frame onto its side, and prop it against a wall away from the pedestal.
Lay the decking on top of the pedestal base, with the cut corner positioned at the corner of the head of the bed closest to an electrical outlet. Measure the overhang to ensure that the decking is centered on top of the pedestal.
Lift and place the frame squarely on top of the decking. The grooves along the bottom inside edge of the frame boards will rest on top of the edge of the decking and hide the unfinished edge of the decking plywood. Measure to make sure the decking is square on top of the pedestal.
Screw two or three corner brackets into each inside corner created by the frame and decking with a Philips screwdriver. Set the headboard on the protruding sections of frame, and secure to the inside of the frame with straight brackets and screws. Test the rail caps to make sure they fit snugly, and then remove them. Cover all brackets on the inside of the frame with duct tape to avoid mattress leaks.
Place the heater pad in the center of the bed. Run the cord through the hole in the corner of the pedestal at the head of the bed. Plug it in, turn it on and make sure it works. Unplug the heater. Place the liner on top of the pedestal and heater. Spread it out, and press the corners into the corners of the frame.
Place the mattress inside the frame and liner, with the fill valve positioned at the end of the bed. Pull the corners of the mattress toward the corners of the frame, and smooth the wrinkles from the bottom of the mattress. Connect a clean garden hose to a fill kit adapter and kitchen faucet. Pull the fill valve from inside the mattress, and remove the cover. Attach the other end of the garden hose to the fill valve.
Fill the mattress. Pull the mattress corners toward the frame corners during the first part of filling to remove any remaining wrinkles from the bottom of the mattress. When the top of the mattress reaches 1/4 to 1/2 inch below the top of the frame boards, turn the water off and disconnect the hose .
Pour water bed conditioner liquid into the fill valve according to package directions. Run the handle of a broom across the top of the bed. Direct air bubbles out through the fill valve. Replace the fill valve cover, and push the valve back into the mattress. Dry any water on the mattress surface with a towel. Plug the heater back in, and turn it on.