Yes, that can be done. Go to Lowes & get a sheet of luan plywood & some 1x4" pine & a sheet of 5/8 or 4/4" foam insulation.. Make a frame with the pine & then glue & screw the luan on the bottom of the box.
Cut a layer of foam for the bottom . Now mark off the width for the next layer. Lay the gun on it & draw the outline of the gun. Take a razor knive & cut the outkine, cut a second outline on another sheet.
Now put some doublesided carpet tape on the bottom sheet in the crate & lay the first outlined sheet in on top of that. Tape, & repeat for the second sheet. Now take an old sheet or some other fabric & take some spray adhesive & spray the foam & press the sheet into all of the rifle inlet & make sure you get into all the corners & come out to the edges with the material & now you have all of the foam covered. OR you can put the rifle in one of those silicon impregnated gun socks that you can get at some places.
Take a top sheet of foam & spray it with adhesive & wrap it in the material. (Keeps it from breaking as easy & crumbling)
So, now you have the foam in the box, the rifle inside the foam in all directions & a foam cover.
Now make a luan or 1/4" plywood lid & hinge it on one side & 4 small latches on the other side.
This is what I ship most of my rifles to customers in. I have the crate enclosed in cardboard, have shipped 40+ rifles this way & no damage as of yet, to the box or the rifles. I didn't hinge it, I just use sheetrock screws to secure the lid cause I am not in & out of it all the time like you would be doing.
Now if you have access to the liquid foam used in shipping, you may be able to fill the box with foam & sit the rifle in it, but I have not tried that & you still need protection on the top, so I would leave 3/4" at the top for padding as well. I know they make it as I get things shipped to me that the foam was sprayed in & etc. But it is more substantial than the cans of foam you use for insulation & etc. that I have tried. :hmm: You might check on line with a place called U-Line as it has all kinds of shipping stuff & may have the foam. And it may be cost prohibitive as well, to go thru all of this...... pretty easy to make a box & sheet of foam & a lil glue & hinges & latches. Put a large handle on on side in the middle of the 1x4 to carry it with. :thumbsup: