Work your players up into progressively bigger and bigger camps. Start out with a few scouts on the outskirts, with one, maybe two, tents. Probably a group of 2 1st level Gnoll Warriors led by an (insert party level here) level Gnoll Ranger, with Precise Shot if level 3+, firing into the party while the Warriors act like the big dumb meat-shields they are.

Then, they start running into the patrols. They don't have tents, players just run into either the day shift or the night shift. Patrols are either 4 Warriors and a Ranger or 2 Warriors and 2 Rangers. If the patrol should happen to see the PCs before they seen the patrol, send one of the Warriors off to a warcamp as warning. Pretty much the same tactics, sniper Rangers, meat-shield Warriors. BTW, if the Rangers have a companion, send one of them as a runner (choose nastiest low level animal in that area).

The warcamps are where it starts getting interesting. Presumably these would be where the tribes other than the queen's would be. This is also where we start seeing slaves. Slaves can be just about any humanoid race you want. The warcamps are surrounded by trenches, possibly with wooden spikes. If you have at least one intelligent or wise gnoll (presumably your gnoll-queen), set up double trenches, with spikes facing both outward and inward (both for discouraging slaves from escaping and for bull rushing pesky adventurers onto ). These guys are mostly going to be Warriors a few levels shy of the group and typically 3-4 Rangers per 10 tents. Give the players an opportunity to sneak over the spikes without getting seen if no runners made it back from patrols, but make it hard. Also, to make it realistic to support such a large populace, maybe put a few crops here. It would be impossible to survive on pillaging alone, but it would also be impossible to survive on farming alone. I'm not suggesting something a normal human farmer would have, like grain or green beans, more wild plants that the gnolls are caring for, like winter peas.

Past the warcamps is the cave. This is the main base of operations, with your baddy at the back. At this point, every gnoll has class levels, and the only slaves are going to be kobolds and dwarves tunneling the place out. At this point it should get fairly tough. All gnolls should be within 2 ECL of your party's average level (both up and down).

If you're like me and want to be as realistic as possible, have the kobolds smuggle you into the slave's quarters when the party needs to rest, as repayment for attempting to kill their captors. You may want to roll a die (pick your favorite) to see if they get caught or not.

Ultimately, it's up to you. This is just my suggestion (based mostly on a campaign I played through). Good luck.