I use a lowe pro mini trekker aw which I'm really pleased with. I had doubts as to whether it would be big enough but it holds my RB67 with 90mm attached, extra back, 180mm, 2 lee filters + hood, 6 screw on filters, pentax spotmeter with room to spare. I really like the tripod carrying feature and the light weight.

Lowe bags are good but the larger ones as stupidly priced, I refuse to pay over 70 for a camera bag.