Are you referring to grub2iso[1]? If so, I was never able to make it work: either the ISO is too large (IIRC, in the old days it needed to load the full ISO to memory), or, if it did boot, the kernel wouldn't find the ISO ("virtual drive") itself.
I only got it to work with simple things that load fully from RAM -- say, debian-installer, which only requires kernel+initrd.
It has to be simple and reliable. If it's only one of them, I would rather carry an extra USB stick which I can always format (I do).
And make sure you've insmod'ed any modules you need for your hardware if necessary (storage, USB, etc.)... unfortunately documentation on these is poor, and some modules are mutually exclusive, so have fun.
I only got it to work with simple things that load fully from RAM -- say, debian-installer, which only requires kernel+initrd.
It has to be simple and reliable. If it's only one of them, I would rather carry an extra USB stick which I can always format (I do).
[1]: https://help.ubuntu.com/community/Grub2/ISOBoot