First of all: thank you very much for your effort on Zeroshell. It’s a very nice collection of softwares, all glued together with great competence and even more nice software.
My suggestion is to use FWKNOP (http://cipherdyne.org/fwknop/) to protect admin interface and/or SSH when used from Internet so it stays hidden from DoS or inconvenient scans while still providing access those that knows how to reach it and are authorised to access them.
FWKNOP is another example of great software that enable even direct Internet access to the admin interface without compromising security. To me it’s a perfect combination.