I'm still partying in the hidden room in Crawlers Nest. You can party there all the way to lvl 50, I've had several friends who have. You may want to take a right in the main soilder crawler room and hang against the right wall. After a while you'll find a hallway w/ rumble crawlers. A goooooood source of exp, but you can often get links there though. As long as you have a Bard and a Blm in your party you're safe sleeping the extra mob until you can kill the second. If everything gets bad, just have your main tank take some hits for 15 seconds while your Blm escapes you out.
If you're still killing Beetles at lvl 47 you're probably getting crappy exp in Quicksand. Try out the Anticans, they can be pretty tough and some of them will use Ancient Magic that'll do 500-700 damage to your main tank, but they're quite doable with a balanced party of 45-46. Exp from those is really good too, we were getting 220+ on exp chains there a couple days ago.