The VP150 is wide enough that it should cross two studs, whether they're 24" or 18" on center. If there's a stud aligned with the middle of your screen, buy one Full Metal Bracket and use it to mount your VP150. If the studs are not aligned, buy two brackets and screw each of them into a stud. The two brackets need not be symmetrically spaced in relation to the VP150.
Alternatively, you can remove a piece of drywall, attach a 2x4 between a couple studs in your preferred mounting location, replace the drywall, and then use a shelf screwed into a stud and the cross piece.
