So I got on the kick that I wanted to get forward and reverse DNS working on my HE.net tunnels. It was probably annoyance at only getting 19/20 here:
http://ipv6-test.com/ I poked around with the he.net dns options, but manual entry is not an option I was interested in and I didn't want to mess around with figuring out if I could get dynamic registrations working. I didn't need anything too complicated, some sort of automatic records would be preferable.
Eventually I stumbled across Knot DNS. The synth-record module was exactly what I was looking for. I got it configured and slapped it on a couple of IPv6-only VPS's. Then I set the rDNS Delegations in the he.net tunnel configuration screen. And it didn't work.
I waited a few days, I emailed he.net about it, and it still didn't work. NXDOMAIN every time. SOA still pointing to ns1.he.net. The eventual solution appears to have been deleting the zones from the he.net free dns management page
https://dns.he.net/ . After removing the reverse zones on the dns management page the he.net dns servers started properly using the delegation information I had entered on the tunnel rDNS delegation configuration page.
So now everything works and I get 20/20 at
http://ipv6-test.com/ . Hooray!
Having gone through the trouble to get this working I also thought I might like to share the rDNS servers. So, if you too want valid rDNS for your tunnels then just set your rDNS delegations to the following:
ns1.rdns.onlineregistration.xyz
ns2.rdns.onlineregistration.xyz
These servers are already configured to respond for any he.net tunnel IPv6 address.
I figure it's one small way I can give back in thanks to he.net for providing the free IPv6 tunnelbroker service. Thanks he.net!