"Unlimited hard disk space" for our Premium servers, and Budget servers quota does NOT include dynmap!
The disk space is intended solely for Minecraft itself. Worlds and function plugins, for instance. Plugins that serve no purpose to Minecraft itself, like dynmap and block loggers, can easily consume 20+ GB when your Minecraft server itself isn't even using 1GB of space.
To install Dynmap for your server, follow the other plugin guide and locate Dynmap. The one you want is named just "dynmap":
Once you've installed the correct version of Dynmap for your server (see this guide for more information about plugin versions), restart the server.
Now use Multicraft to edit the configuration file. Click on Files, then Config Files, and then locate the configuration.txt file in the dynmap directory:
Now change the port number to a random value between 8100 and 8200. This setting is about 3/4 the way down the file and defaults to 8123. (DO NOT USE port 8123, as someone probably has it in use already!)
You also want to make sure that the webserver-bindaddress line is commented out (has a # as the first character), otherwise dynmap will not work.
You'll also need to change the template set to lowres to prevent wasting gigs and gigs of hard drive space, which will lead to automatic server suspension for disk space and CPU abuse. (Rendering hi-res tiles is very CPU intensive.)
Now restart the server and visit http://your.servers.ip.address:45786 (or whatever you set the port as)
It is normal to see an empty map to begin with, as it takes time to render.