These will be pictures of my solid (basic) bottom boards. (Apologies to the SBB folks, I stopped using them)
Rip some pine into 7/8" thick x 2" wide strips.
Cut them into lengths of 22" (sides) and 16 3/4" (ends).
Then, using dado blades (stacked just over 3/4"), cut some troughs down the length of each pieces, leaving 3/4" on one side, and 1/2" on the other. Make your cuts 7/16" deep.
Then, on the end piece (16 3/4") cut in from both ends 7/8", 7/16" deep. You should end up with ends looking something like this.
Lay out your pieces and glue and screw them together. I find pre-drilling the screw holes helps avoid splitting.
Now you want to find some 3/4" t & g and cut a bunch 15 3/4" long.
At his point I usually rip off the tongue of the first piece and just start stacking them in the frame you've just built. Sometimes a rubber mallet helps persuade them. You can lay glue in the trough if you want to.
I then just put a screw in the end of each piece through the side rails and.........it's done!
Like anything, if you're making one, why not make a few? The time involved in setting up is minimal and the material isn't that expensive.