I saw the review that said it was 1/2" MDF and I think that would be the sides. 1/2" isn't thick enough for a baffle to be really inert unless they doubled layered it. 3/4" can be resonant enough and I have tried using 1/2" with bracing and it didn't make me happy.
You could do this several ways, one being #12-3/4" flat head screws (assuming the outriggers are countersunk. These come in black and are available at Ace Hardware stores. If they're all laid out the same, they will be at the left end of the aisle with all of the screws, nuts, bolts and other fasteners. As long as you pre-drill with a 1/8" or 3/32" drill and screw them in by hand, these will definitely be enough to hold them in for a long time.
The out riggers don't do any more than add stability- they don't need to be held in permanently and in normal use, the screws will never come out.