My personal grub.cfg backup, and public reference for anyone who wants it.
This set of .cfg files and associated scripts is set up such that all files are kept on the root of the drive, and .cfg files are copied to the appropriate place as required. I've found this allows for easy editing of the .cfg files when adding a multitude of new ISOs.
If you want to use my configs, the only thing you need to change is the UUID ($rootuuid) of your device in grub.cfg and reinstall_grub.sh.
All options thus far built by myself using various forums scattered across the internet.
If you have anything to contribute, or if you know of a way of doing things better than what I've done, please let me know. I'd love for this to become a decent public reference point for creating a bootable USB.