• Ape Atoll •
This is currently the best place to train with Red Chins. To be able to get here, you must have completed the Monkey Madness quest. The location is on the same way you passed through when you wanted to get to the end and speak with the mage, Zooknock.
Here's how you get there. Teleport to Al-Kharid. Head to the Gnome Glider and choose the big tree so it can take you to the Grand Tree. Head down two levels. Go east and speak with Daero. He will teleport you to some type of dungeon. There will be a Gnome north. Ask him to take to you Crash Island. Once you arrive at Crash Island, there would be another Gnome named Lumdo. Ask him to take you to Ape Atoll.
Once you arrive Ape Atoll, head west until you find the '!' symbol on the mini-map. This is the dungeon you're looking for. Once you feel ready go in. Further information will be available later.
For me, I chose Ape Atoll. Monkey Skeletons are higher in Combat and thus, they give more experience. It is up to you though.
• Chaos Tunnel •
Here come the mummies. These are great experience, almost like Ape Atoll but there is still better. Mummies are level 103 and they have lower Hipoints than Monkey Skeletons at Ape Atoll.
This is the fastest way to get there. There's a dungeon directly south of the Chaos Altar [RuneCrafting one]. Go there and enter. Head west. You'll see two portals. You'd want to use the northwestern one. After you enter, head west and you'll be at mummies.
Mummies drop items that can be used to pay for the supplies used.
There may be other places but I consider these two the most popular ones and the best.
http://forum.runescape.com/c=mlcSLnGqG7E/forums.ws?98,99,254,58152009