never really used marine ply but you should really pre-drill regaurdless of wood type..... it is a good habit to form. Weather you you HAVE to are not I dont know
The biggest time-saver you can get is a set of right-angle clamps (aka framing clamps), and a countersink bit. Get the bit that has the drill bit coming through it. I got cheap Craftsman right angle clamps for like $10/pair. The countersink bit should cost you about $5. That bit predrills your hole, and carves a countersink for your drywall screws in one step! Makes box building a several-hour affair, rather than a several-day affair!