[Mac Fellow]

I use a Kensington Saddlebag for my PBG4 and it suits my 'low impact' needs pretty well but I'd perhaps consider the Dr. Bott TiCase if my budget allowed.
http://www.drbott.com/prod/db.lasso?code=5803-TIBC

It's definitely NOT CHEAP but the DrBott web page suggests that it might have been 'endorsed' by James Bond for hopping off balconies in 'The World is Not Enough'