Take a look at this one posted awhile back, there are no plans but it is a good design and should give you some ideas.
Tim C.
http://americanlongrifles.org/forum/index.php?topic=4855.0
Hey! That's my box! I clicked into this post hoping to see someone's new box.... haha.
On my box, I sorta made up the plans as I went. I don't have a table saw, joiner, planner, etc. so I bought dimensioned oak from Lowe's. I think they call it "craft" wood and it comes in 2, 3 and 4 foot lengths of various thickness's. I used 1/2" thick for the box sides (so the dovetails would be bigger) and 1/4" for the top and bottom of the box and the tray. At least I started with good square pieces and used all hand tools from there.
In hind sight, I could have made the bottom of the box a little bit shorter without losing too much storage area. As tall as it is, I'm carrying around about an inch and a 1/2 or so of air.
-Ron