To create a DNS based seed (I'm not sure about the words) you need to have a domain name, and after create a subdomain.
This subdomain will have some A record pointing to IPs address running HBN daemon.
For example
seed.domain IN A IP.HBN.1
seed.domain IN A IP.HBN.2
etc...
you can add some AAAA fields if the daemon have IP connectivity.
It's not complicated.
For me, I'm running 3 HBN daemon, on 3 differents servers.
host -t A seed.scrypt.io
seed.scrypt.io has address 5.39.90.17
seed.scrypt.io has address 91.121.177.181
seed.scrypt.io has address 176.31.250.94
and :
seed.scrypt.io has IPv6 address 2001:41d0:8:b5e::1
seed.scrypt.io has IPv6 address 2001:41d0:8:9c11::1
seed.scrypt.io has IPv6 address 2001:41d0:1:f2b5::1
If you are running on static IP the daemon, you can give me the IP and I can add it to my "seednode", but if you're running multiple daemon on multiple dedicated servers, you can create your own seednode.