Not sure about the boot bag - I tried one last year and found it's soft underside not that great on a Morgan rack. Plus all the buckles / straps to do up / undo became a bit of a trial. Not too bad if you are going to be based in one or two places, but on an everyday basis would become tiresome. That said, I'm holding on to my Bootbag for use on a car with a small boot...
I recommend a waterproof case, such as a Peli case.
Jays has done most, if not all, of the Western Isles, mainly on 2 wheels, so might be able to give you some geographic pointers...
