You can get the iso here: https://www.caine-live.net/page5/page5.html

I use makeUSB.sh to get my usb multibootable, and copy the iso to isos/ directory, then copy ubuntu-18.04.1-desktop-amd64.iso to isos/ as well for compare.

And for the purpose to make caine bootable, I mkdir in mbusb.d/caine.d, then copy the config of ubuntu in this dir: cp ../ubuntu.d/desktop-generic.cfg ./caine.cfg, and then modify to:

for isofile in $isopath/caine*.iso; do
if [ -e "$isofile" ]; then
regexp --set=isoname "$isopath/(.*)" "$isofile"
submenu "$isoname (loopback.cfg) ->" "$isofile" {
iso_path="$2"
export iso_path
search --set=root --file "$iso_path"
loopback loop "$iso_path"
root=(loop)
configfile /boot/grub/loopback.cfg
loopback --delete loop
}
fi
done

but it will cause some error occurred like this:

error screenshot here

Actually, ubuntu works! but caine is based on ubuntu, I don't know why caine can not work