I don't remember any chapters stated to operate from a Space Hulk.
Soul Drinkers, after their break with the Imperium.
Probably because fluffwise they have an unfortunate tendency to enter and leave the Warp at random, Gellar Fields not included.
Again, bearing in mind that everything is possible in 40k, this is not strictly true. Individual ships that make up a space hulk can his have active generatoria, plasma drives, warp drives and even Gellar Fields. The Gellar Fields only need to malfunction in the warp for a ship to theoretically become part of a hulk, not be completely non-existent. The reason hulks randomly jump into and out of the warp is because they still have active warp drives, multiples, doing random things, being run by an insane machine spirit, etc...
The Soul Drinkers novels gloss over some of the specifics, but basically with an assload of cabling and several years to work, their Forge Master essentially wired all the disparate functioning parts of different ships in the hulk together and slaved them all to the helm in one of the better kept ones. Other than not explaining how you merge several large machine spirits like that together without committing a tech heresy (or how a Tech Marine Forgemaster pulls off a singular feat like that without knowledge and help directly from the Mechanicus), it's feasible.
And let's not forget, Orks do it all the time by the power of being Orky.
Including spaceborne fortress-monasteries, a la the Phalanx, would be fun, but as far as I can tell simply making the big tough ships wouldn't be very accurate.
Well, space battles in 40k are not exactly straight forward nor modeled directly after other GWS game mechanics. The game doesn't really account for void shields, which if it did, would put a distinctly different spin on Space Combat. The whole idea is that void shields prevent all damage until they fail, and then it comes down to hull strength and the class of weaponry. By all rights a Strike Cruiser hit by the kinds of large primary weapons battle barges field should wreck it only a few shots. Anything smaller would be pretty much instantly obliterated.
You know, this has me thinking. Space Combat would be a lot more interesting (rather than usually feeling like a slug fest) if damage were modeled with more detail. Disabling weapons, disabling motive capabilities, crits leading to plasma drive breaches, ammo explosions...not to mention trying to factor in void shields, would make combat feel like it has a lot more depth. It would require a way to get messages to the player though, those notifications wouldn't really cut it for the kinds of details you'd need to tell the player.