If we change the ISO location to other USB partition:
set isopath='(hd0,msdos2)/isos'

There is a problem showing the name of the system at boot time in GRUB's menu.
I think is a problem with this line in the scripts:
regexp --set=isoname "$isopath/(.*)" "$isofile"
I suppose that is because of the round brackets "()" of the path.
I don't know which is the best solution for this issue, I have fixed it replacing the line with this one:
regexp --set=isoname "[$isopath]/(.*)" "$isofile"
But I don't know if this could be a problem in other situations.

Thank you very much.