Take your 2x2x8 SPF and cut it in half length ways on a 45° angle with a table saw - you may also purchase pre-cut Chamfer Strip, but I chose to make my own. You will need two right-angle triangular pieces for each 8 foot bass trap.
With your plywood, mark out a right-angle triangle woth a hypotenuse of 2'. Cut out three of these per bass trap. Take one of your 3/8" plywood triangles (which will become the middle support) and trace out each of the vertical columns onto it - a triangular 2x2 in each of the triangular corners, and a regular 2x2 in the remaining 90° corner. Notch out these markings from the plywood pieces.
Place a triangular 2x2 in each of the remaining two triangular corners of the 3/8" plywood cutouts (which are now the top and bottom), and attach them with 1-1/2" wood screws. Use a regular square 2x2 on the remaining 90° corner, attaching to the top and bottom as well.
To anchor your middle support, place the notched triangle within the frame (4' from the top and bottom) and attach with 1/2" screws and three metal right-angle brackets.
Important: The point of the middle support is strictly to minimalize the compaction of the insulation over time, as it effectively cuts the weight on the bottom pieces of isulation in half.
Now that you have your completed frame, start cutting up your insulation with a carpenter's square and rockwool saw. If you are building 2' (hypotenuse) bass traps, cut each piece into 8 equal triangles. One 2' x 4' piece of Safe'n'Sound will yield 24" of vertical fill, which in turn means you will require 4 full pieces of Safe'n'Sound for one entire 2' hypotenuse 8' tall SuperChunk Bass Trap. You will need 8 full pieces if you are creating 4' hypotenuse 8' tall traps. Stack a bunch of insulation triangles, then run your rockwool saw down each corner to trim them for the frame.
Begin filling your bass trap. Once you approach the middle support, as well as the top, stop just shy of the plywood as to not compact the insulation. Use some of the corner off-cuts to lightly fill the remaining space.
Important: Never compact the insulation too tightly by stacking your frames with too many insulation pieces, as this is actually counter-productive and will cause a significant decrease in effectiveness. Absorbers work by the sound waves moving around particles in the insulation, which in turn converts the sound waves into heat. Remember: you can never destroy energy, only convert it to another form.
Take your fabric and cut it into appropriate sized pieces. Total width of your main covering should be the hypotenuse of your absorber, plus two times the side length of your absorbers, plus two inches (an inch over hang on either side for stapling). Use the basically same formula for the height. Staple the fabric on the rear corner.
Important: When selecting your fabric, ensure that it is breathable. The best test is to put it up to your mouth with your palm on the opposite side, and breathe into the fabric as if you were going to clean your glasses (Haaaaaa). The more air you feel on the opposite side of the fabric the better. This will ensure the sound waves are making it through the fabric to your absorbtive insulation.
Place the SuperChunk Bass Trap in your corner. If you are planning on them being a permanent installation, I would suggest getting some moulding and framing them into place giving them a nice finished feel.