You got already the rear Kaymar (I guess with the tire carrier) and the dual filling neck so you have almost all the hard job done (and a lot of $$$ spent).
Sell your subtank with straps (you have it in the States so this is a big selling plus) and get ASAP at least a 120 ltr tank because...
If I were you and had already installed a rear bumper tire carrier and all the OEM dual neck gas filler and related plumbing, I would sell the subtank and source a long ranger 120 ltr aux tank with a compatable OEM sender. That's more than twice what the OEM sub tank carry.
Of course...