I remember I made one side cutaway drawing of a multilevel underground base staffed by Pac-Man ghosts and being invaded in real time by Pac-Man commandos!
I note the one thing left out of the fort elements is a restroom - best invest in some of those portapotties! 
...Awesome! 'Love the idea of the invading Pac-Man commandos! So the ghosts were the good guys?
...Do you still have it?
Re. restrooms: Yes, you're right; I remember always putting restrooms in my cross-section bases, as a kid. I should have mentioned them in the list of key fortress elements. Call it 'waste disposal', broadly speaking. Though, in the Spy Team base,
they are included ( inside the barracks containers: set 5051 / 3260 ).
Re. Navarone playset: it was a source of inspiration for Mattel's
Castle Grayskull playset ( see:
The Toys That Made Us series / He-Man episode, on Netflix ).
For laughs, here is a self-burying base I did 4-5 years ago, to inspire my nephew into thinking about drawing his own, reminiscent of the kinds of base/fortresses I used to draw as a child. Though back then, I'd draw them in 2D and
with weapons. Note: I initially nearly put a canon at the top, instead of the radar, but changed my mind in an attempt to set a good — pacifistic — example ( I was wrong! ) ...Toilets included, of course!
