I've posted some PRs to resolve the issues with building Ubuntu
templates.
If you can't wait for them to be merged, and want to try Ubuntu I've
posted some minimal templates here:
http://qubes.3isec.org/Templates.
The templates are signed with my Qubes signing key.
You can get this from keyservers.
I certify it is mine at
https://github.com/unman/unman
I'll be putting in PRs to enable bionic builds in next day or so.
unman