Ok, I have my bolts, nuts and washers. I went to Lowe's and I purchased 6-32 x 1 1/2 stainless steel slotted pan head machine screws. They are a bit long but the only other size was just not long enough. The nuts are 6-32 lock nuts with nylon insert and the washers are #6. The screws will actually thread through the mount providing a bit more strength. I am placing the washer on the head side of the screw with no washer on the inside of the box since it has a lock nut there.

One thing I did to "prepare" the mount was to drill through the mount without effecting the hole walls. I used a small drill bit to just "punch through" the hole on the top side. I used a 7/64 drill bit for drilling through.

Now I had a hole all the way through but the hole was too small to allow me to start my screw (the 6-32 SS screw) from threading. What I did now was to enlarge or "ream" out the surface of the hole with a larger drill bit. I only did the very top of the hole and I used a 5/32 drill bit for this. Now I can start to thread my 6-32 screw (don't forget the washer first).

I am now going to install the box......photos to follow.