-Spare 2x4's, cardboard from the shipping crate, and spray adhesive from the foam rib templates.
I started with just a simple "H" shape of the 2x4's but ended up adding one more 2x4 in the middle of the "H" to provide support towards the rear of the c-frame. I could have done without the extra if the "H" was longer but I didn't have enough wood to do both sides so I figured this would work.
As it turns out, the whole set up worked great. I was worried about the sturdiness of the cardboard but as it turns out it was a non issue. The best part about the whole thing is that it is extremely light and easily stored on the top shelf!