If you need to put it in another enclosure then I'd try and make that sucker fairly dense to keep resonances to a minimum. Won't be optimal, but better than no sub at all.
Here here... Surely we all want the best sounding HT we can build/buy. For some of us there are zero restrictions holding us back, others have certain trade-offs to contend with. If it were true that it wouldn't be worth putting together a HT if you couldn't do it optimally then I wouldn't have a HT right now because our HT doubles as our sales/presentation room, and therefore has many compromises built into it.
But it's still amazing to watch movies, listen to music on! It could be better, but I'm not complaining.