Think siege mod is a huge pain in a cave world since not only are they tunneling to get you they're also making unlighted areas to spawn more mobs at the same time. While floating box strats work they seem exploitative of limited AI, not really within the spirit of the mod.
Hmm, used the dungeon caller. It dropped me far enough to take half my health, landed me in the dark on top of a mob spawner between water and lava. Of course the lava spawned lycanites mobs that I couldn't get away from and I died. Upon respawn I'm not at my bed, much less my base. As far as I can tell I'm nowhere near either of them. Kind of frustrating.
How is it exploitative?
Epic Siege Mobs can still see you using X-ray. They can still mine through the ceiling, drop on your roof and start trying to dig through (which is why I advised building your box with murder holes so you can attack things on your roof). They can still noobpillar up and try digging through your floor (same thing, leave holes you can strike down through). They can still bridge sideways to your box and attack the walls, and you have to be ready to stop them there.
It's no different from building a barricade or lining the walls of a cave with obsidian except that you can (1) see the "outside" of your wall and hit them before they finish mining through it and (2) by building a small box you ensure that phantoms have to be in your sword range before you can hit them. You MUST actively defend it or they WILL come and kill you. You can't build the whole thing out of obsidian and just sit in it or sooner or later you'll open the door to ten thousand slimy, slimy things that've been waiting to say "Hi." Not to mention at least some of the mobs have diamond tools and apparently can break obsidian.
Drastic has included turrets for tower defense. If you don't build a base inside an open area, those turrets don't have anything to defend. Barricades are a part of tower defense. Drastic even changed the Dark Power quest line to allow you to purchase obsidian directly, rather than hunting obsidian-dropping mobs. I don't see how using that obsidian to create buildings with walls that take longer to break isn't within the spirit of the mod.
I don't see how this is more exploitative than any other building strategy. When you say someone is using an exploit, you're effectively saying they are cheating. I don't rightly appreciate that insinuation, sirrah.
You are welcome to play the game however you like it, of course, but please don't tell people who are using fairly straightforward defensive structural tactics (why call them "siege" mobs if there's no defensive structure? "Siege" means to assault a fortification!) that they are cheating or "not in the spirit of the mod."
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NOTE FOR DRASTIC:
...And speaking of "exploits" which are nevertheless a part of standard minecraft strategy, in my latest let's play I realized that apparently the endless spring trick (2x2 hole, diagonally opposed water source blocks) has been disabled. The only time I've ever seen that done before was Crash Landing, and since this isn't a thirst-based mod I'm curious about it. Is that intentional, Drastic?