18.04 is missing package versions we need in its repositories. We need to manually install the versions we need. I fetched the following from the Debian stable repositories, the webpage https://packages.debian.org/index with Debian Buster as my distribution:
clevis
clevis-luks
clevis-tpm2
tpm2-tools
libtss2-esys0
libtss2-udev
Manually install these with dpkg -i after running step 0. Once installed, I recommend a reboot then continue with the typical installation process.
These versions have the packages we need. For TPM2, run apt-get install tpm2-tools clevis-tpm2 clevis-luks after ./0- and perform the rest of the steps as normal.