My approach to the fit and finish of the woodwork was mixed. I like a good fit - the lid should fit properly and, as much as possible, the transit case should keep out dirt. As to the finish, it is, for all practical purposes, a shipping crate. I used course sandpaper to knock the sharp edges and fuzz off the finished box, but that was it. I didn't worry about saw marks.

The list of materials needed is short:
1 x 6 x 8'   (5)
Handles (2)
Hinges  (2)
Lock hasp  (1)
Latches (2)
Lid support (1)
Drywall screws - 1 5/8" and 1 1/4"
Wood glue
Wooden pegs or dowels

   Rip 1 3/4" off three of the 1 x 6s to be used for bracing and skids.
The sides and ends will be made from one length of the remaining 3 5/8" and one length of 1 x 6 (1/8" was lost in the saw kerf). The end boards are all 9 1/2" long. The top, bottom, front and back boards are all 45". The top and bottom are made from two 2 x 6s.
   A 1 x 6 is actually 5 1/2" wide, so the top and bottom are 45" x 11", the front and back are 45" x 9 1/4". The ends are 9 1/2" x 9 1/4".
   I put the wider board on the bottom so when the handles are installed on the ends, two screws will be in each board.

List of cuts:
1 x 6 x 45" (6)
1 x 6 x 9 1/2" (2)
1 x 3 5/8 x 45" (2)
1 x 3 5/8 x 9 1/2" (2)
1 3/4 x 9 1/2" (4) vertical braces
1 3/4 x 11" (3) bottom skids/braces
1 3/4 x 9" (3) lid braces
Glue joint and clamp while
installing vertical braces. Scrape excess clue off, don't wipe unless you use a wet rag and do a thorough job. Any glue left on wood will ruin whatever finish you decide to use..

Because the front and back panels have no vertical braces in the center, I added two fluted pegs in each pair to keep the boards in line and add some strength. A centering jig is helpful, but not required, so long as you make certain to measure for center from the same side (inside or outside) on both boards.
NOTE: Glue the joint between the boards only - do NOT glue the cross braces. You want the panels to have some give, "float", otherwise seasonal swelling and shrinking will cause the boards to crack. Except for joining the boards, I used no glue in this project.

Rather than wrestle with a lot of bar clamps, I sometimes alternate with strips of tire inner tube. Pull tight with each pass, then tuck in the end. The strip is about 1 1/5" wide and 6' long. It builds up a lot of tension after a few passes. And cheap. The cabinet scraper I used to remove excess glue is at top of photo.

Peg is off center, but matches
the hole in the other board, so
they lined up nicely.
A C-clamp holds end in place while securing with screws. I used course thread drywall screws. 1 1/4" for vertical cross braces and lid cross braces so the screws won't pop out the other side, and 1 5/8" screws everywhere else.
After the front, back and sides have been assembled, I laid out the bottom. Screw one board in place, then glue a long edge of the second board and clamp it in place.

Now, to remove the hardware and paint, then layout the inside. I ultimately chose a chain over the lid support.

Start at one end, and as you move down the box screwing in the second board, screw the bottom skids in place to hold the boards together. Use 1 1/4" screws on the center brace.

The box, after installation of hardware.
Keep the lid support bracket lower connection point as far back as possible so it does not interfere with gun on armorer's mount when open.

In the enlarged photo you can see that the lock hasp was let in on the underside of the front lip of the lid. It's a good idea to keep the screws out of sight. This is hardly a heavy security box, but it's nice to be able to keep out the curious. We'll call this security level pink - probably can't be broken into with a nail file or a plastic spoon. Swiss Army Knife - maybe.

The hinges I used are the "T" type. I bent the strap over the back lip of the top, then swung the butt hinge side under the lid, beveled the back side of the plate, and screwed it to the top edge of the back board. I let it in with a chisel so the top will seat nicely.