Just to clarify, is this going on the RHS as a dummy exhaust ?
The pics below are from AdvRider.....
I found a length of 150mm dairywall but the 100mm would match
the silencer better if it's to match the silencer, your call ??
There used to be loads of XChallenges down here before that I could have taken measurements off, but they've all be sold on.
Regarding mounting it, the further back on the tank you mount it the better, when full of fuel it'll be bloody heavy.
Before I cut any holes for the cap I'll see if I can find a vented one, it won't be lockable though, unless you have something
we can butcher up.