Change the Peplink Balance /cgi-bin/MANGA/index.cgi login page to allow the (Firefox) browser to save the username and password.
Is is cumbersome that the admin needs to hack the html of the login page using firefox - Manually add username/password to Saved Password list? - Super User to be able to save the username and password in the browser.
<button type="button" tabindex="3" class="submit_action">Login</button>
should become something like:
<input type=submit>
Hello ProBackup,
We have not have seen any issue with this on Chrome, IE or Safari from our tests (we do not use Firefox currently).
In terms of managing web admin passwords securely we use for our teams the Enterprise version of LastPass, as long as you adhear to the best practices and used 2nd factor authntication and follow the guides they have, we can asure you it works with all of the Peplink/Pepwave family.
Happy to Help,
Marcus 
FWIW, we use Firefox and, as @mldowling suggested, use LastPass to manage the log-in credentials. Works perfectly. Even the free version of LP works fine, although we use a paid version.