This the one that I have and it fits great. I also have the Proline Dodge Mega Cab, but it is a little short. They are both for the LST, MGT, Genesis ETC. Link feature won't work but you can copy and paste.
Any of the LST/MGT size bodies will fit the XL perfectly. When I ran the full extended IRC chassis I use those bpodies. Stock Savage X bodies look too short IMO on an extended rig.
Edit; The body in my Avatar is the long bed C10 from Proline for the Revo 3.3. Most of the Revo 3.3 size bodies fit lengthwise but are narrower.