Set the propane heater on top of its base and set the base upright on the working surface. Shut the heater off. Position four 18-inch 2-by-4 boards around the base. Arrange the boards resting on their long, thin edges. Set the faces of the boards against the heater.
Adjust the spacing of the boards so they are even, with part of each board forming a small box around the propane heater and the other part sticking out in all four directions to stabilize the heater.
Drill two holes through the outside surface of each board and into the ends of the board that adjoins it. Attach the boards by screwing 3-inch wood screws into each hole.
Remove the frame from the heater. Measure the size of the square frame at the center of the stand. Transfer these measurements to a 1/8-inch thick board. Cut out the boards to fit the measurements. Set the square board on top of the stand so it completely covers the hole. Drill holes every 3 inches through the board and into the stand. Attach the board to the stand with 1-inch wood screws. This is the base of the stand.
Flip the stand over and re-insert the heater to use.