What do I need to tow 5th wheel with RAM 2500 Megacab?

Don't have a MegaCab but do have a 2007 Dodge Ram 6.5' bed. I opted for the SuperGlide hitch. More expensive but worth it. I got the rails that mount under the bed to the frame. The entire hitch assembly is held in with pins. This allows me to very quickly remove the hitch and have a clean bed with no rails when needed.

You'll need to measure the 5'ers height over the trucks bed rails and to see how much height is available for the hitch you purchase. The SuperGlide can be increased in height but not decreased.