OP: If you're already using Caddy, why not just use a purchased domain (you can get some for a few dollars) with a DNS-01 challenge? This way you don't need to add self-signed certificates to your trust store and browsers/devices don't complain. You'll still keep your services private to your internal network, and Caddy will automatically keep all managed certificates renewed so there's no manual intervention once everything is set up.
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