I plan to use 4 L-brackets underneath, 2 on each side to attach my control panel to my cabinet. What I'm going to do is drill 4 holes up through the bottom of my control panel where the L-brackets will attach it to the cabinet, then insert a machine screw up through each hole long enough to protrude through the hole half an inch or so and lock it down with a washer and wing nut from inside the control panel. That way it will be secure while it's attached, and I won't need any tools to remove it. I'll just have to loosen the wing nuts, remove the bolts and lift it off the cabinet. I'm also thinking about inserting 4 dowels sticking straight up to help align the control panel and prevent it from shifting side to side while in play. Or maybe inserting some hangar bolts into the cab where the back of the control panel makes contact, drilling a couple more holes through the back of the control panel and using wing nuts there as well.
Honestly what I've been doing is taking a walk through the fastener and hardware section of my local hardware stores, seeing what they have and brainstorming, coming up with ideas about the best way to do everything I still need to do. You'd be surprised how much easier it is to have a revelation about how to solve your problem just by going to a hardware store and having a look around. You'll come up with ideas using parts you never thought about.