actually there’s some command that you should’nt do, but even if you do it have no harm, so I think you must fail somewhere.
I’ve decided to rewrite a complete full guide about this step in Advanced Qubes Installation (light installer / 4Kn Debian Template / Detached header / Encrypted Boot / Dom0 & DispVM in tmpfs) part 2
actually wipefs -a is enough, it would erase crypt metadata too.
you may want to try using iter 1 first for practicing while wait for me to rewrite better guide.