I had a 1x12 board laying around. It is about 4 feet long. I sanded, stained, and sealed it, then using slingshots for a guide, drilled holes at about a 20 degree angle spaced a bit more than the width of my widest slingshot handle. Next I cut 3 inch lengths of dowel rod and inserted the pieces into the holes. My rack holds 16 slingshots, and I have some knotty pine that will make a really nice rack for more when I get back home.
It would be better if I could show you a picture, but I'm in NC until early December. If I can get my wife to snap a shot and send it to me, I'll post it.