Sure, it's feasible but there are a couple of things that pop to mind.
1. Do you have a BIG BOX GOSM? The one in the picture below measures 24 x 36" in size. I tried this trick with a Master Forge 2 door which of course is much smaller, and could not get it to work plus the metal of the Master Forge was much lighter than the BBGOSM and really required a support system that turned the Master Forge's portability to not very useful.
2. Insure the tool box is NOT galvinized (can't imagine it is but you have to be sure).
3. Weight of tool box hanging on the side of GOSM. GOSM metal isn't very thick and could easily be distorted. Think how you're going to support the box.
4. When I hung the SFB on the side, I fought smoke leaks around the join area until I added A LOT of high temp sealant and added some larger bolts with fender washers to give a bigger holding area for the bolts.
In the above vue, you see the SFB attached. Under the SFB is the support which has been integrated to the shelf system I used to get the GOSM up to an elevation that I can work with (bad back problems).
One thing to make sure you do is when you remove the vent shutter from the GOSM, be sure to save the material (in case you want to return the GOSM to factory condition) or perhaps utilize it in the adaptation of the toolbox.
Perhaps a picture of the toolbox would help us give you more information.
Do you have an
AMNPS yet? The footprint is 5 3/8" x 8" x 2".
Height adjustment? Instead of a rack, put a brick in. As long as the
AMNPS isn't flaming, you won't generate enough heat to bother the brick.
Don't give up making it work. It took me several attempts before I got to where I am now. You too can own a FrankenGOSM.
~Dave