Hey Guys,
The Bagster setup was the first thing I had for my FJR (got it befor ehte bike arrived even). I was more than just a little disturbed at the fit initially and thought "There's no way in hell this thing will ever conform", but it eventually did. Sparky has it pretty much bang on... ride it for a couple days, let it sit out in the sun for a few hours and then tighten it down a bit. Repeat every few days and it'll eventually settle in like a custom made glove. Use the fill cap cut-out to align it... it should ALWAYS be round, not oval. At the start, it's okay for it to be a bit low or high, but keep it round as much as possible. You'll fnd with a bit of experimentation which straps deform the gas cutout in which directions. Once it's settle in and gotten the right shape, it's no trouble to get it perfect every time you take it off (which is every two months or so for me, mostly just to check that nothing got under there - nothing yet).
IMO, Bagster is THE BEST tank bag and cover setup there is. Worth every penny and then some.
Sparky, what bag did you get? I'm looking to get another but want to make sure I don't get the one you have... I'm looking for one slightly smaller. I have the Athena, which is one of the "rounded" ones. I prefer the older squarish style like yours. They keep their shape better.