Hey Ripas, I can actually update this myself because I fitted mine myself. The tanks goes just in front of the Axle, in fact Jayco actually make provision for it by setting up the cross beams to allow for the tank to slide in.
I grabbed all the genuine stuff from Brisbane Camperland, including tank, mounting straps/saddles and the stone guard. Cost a few hundreds bucks from memory, I'm pretty sure I detailed it all in one of my earlier posts.
Cheers,
Jason.