I've had some problems with their gear over the years, and in All cases they "went above and beyond". I like what some other companys are building but I trust Sound Devices.
You might want to try a "Drilltap" Just use a battery drill on LOW speed and you'll get a 10/32 taped hole in one shot. On Amazon lookup "greenlee DTAP10-32". Don't force it just let it do all the work, use them all the time.
Walmart carried them at one time, try travel supplies near toothpaste. all kinds of colors. clear, blue, green, purple, etc. they were .99/each. good luck
I've bought 4 of the no name grey NP1 li-ion packs. they worked great for about 2 1/2 years. Seemed to last as long as my IDX's. But went the DIY route this time when I found 14.8v (4 cell) 4.0 Ah Li-ion pack for $40 ea. charger was $25. takes 10 hrs. to charge but bought enough to rotate them. Fitted them with TA-4 connecters that plug in to my distro. system. Found mine on ebay from a company called "Victoriz.com". I have no connection to this company.
Cheers, Steve
Another clean way to mount the box to the cart is to use a "drill tap". Its a drill and tap all in one
just use a battery drill to run it through, install a screw and or a nut your done.