It's a fortress, right? So give it special shield and armor mounts... to make my standard weapon platforms cheaper, I often leave out the combat sensors and design a "Command Center" with just the computer core, combat sensors or Religious Talisman, and lots of armor or shields (to make sure it has more HP than any other platform, so it gets hit Last), and build one on each planet. This works especially well in Proportions with its 100kT, 4000-mineral Fire Control Centers! Wouldnt' want one of THOSE on every platform!
So anyway, you take this fortress and make it your command center, fill it up with lots of armor with a special mount, and you've got something that's guaranteed to get hit Last, and when it is, it can hold out for a while!
