I use a custom domain for everything....email, internal dns, external (cf tunnels), and my public websites. I use to use AWS Route 53 for everything because of work, but moved to CF because it's free and much easier to setup and manage.
For local devices I use *.local.domaingoeshere.com (wildcart cert), issued by cloudlfare. In retrospec I should have used *.int.domain.com as it would be less typing...but everything is categorized and bookmarked anyway.