well too complex in you said the ends were inspired by "a minigun". that just says that you didn't really look at too many reference pictures that you already confirmed ^^
i think what works really well is just randomly browse valves model and look out for models that kinda have a similar theme/look/scale to what you want to achieve. for that "melting pot" or however it's called, i'd say in "props_spytech" there's the rocket_clamp.mdl or rocket_tower.mdl. or in "props_hydro there's hydraulic_door.mdl
or lots and lots of the silo, pipes, tanks or chimney models.
they all are rather "simple models" with a quirk here and there - maybe it be texture or model-wise. anyways, if you just search the right words (which i often don't know either, since i'm no native speaker) you'll stumble upon real objects in google that would fit right into tf2.
i would really try to search a proper reference picture of the approximate time era and then just try to model this and incorporate some of the tf2-style. because what most of the tf2-objects have in common is that they all look kinda believable and functional in their world. no object says "hey my front was inspired by a machinegun", you know what i mean ?
but that's a lot of blabla, i'm sry
