For those who have asked, these are the dimensions I used. I would suggest just making the top 48x48x25 just to give some margin inside the box.
TIP Cut all your panels as shown and assemble the box... THEN cut out the door. That way everything will stay aligned when the door is cut out. Its also much easier than trying to cut all angles for the door individually.
I just rabbited all of the joints halfway through the 3/4" sheets using a dado blade on my table saw. The top, sides and top side of the torsion box are 3/4" maple plywood. The slats and base of the torsion box are 3/4" MDF. The window is 3/8" acrylic but I would suggest using polycarbonate so it can't shatter. The Torsion box may not be necessary but I wanted to have some extra assurance that it wouldn't twist over time. We'll see if that works out or not. I left the outside edge open so I could use the bottom sheet of the torsion box base as a shelf to hold tools and parts.
I used Franklin International 2892 Sound Sealant to bond all of the box joints. It acts as a damper but I don't know if it helped or not since I don't have anything to compare it to. I then clamped the box panels together and used finish nails to hold it. Nothing fancy.
The windows are held in with the sealant also.
Like I said, I would use the full 48x48" size for the top panel just to give some breathing room. Making it taller inside wouldn't hurt anything either.
I just got a piano hinge from Home Depot to secure the door and I used a very strong magnet and a piece of steel tube to hold it shut when its closed.
The gas springs were left over from another project but I know they are 50 lb gas springs from McMaster.com. I think they are about 19" long when extended but I'm not sure. I played with the positioning until I was able to get the door balanced through most of its motion. I can give some dimensions for the mounting points for the springs. Feel free to ask.