Well, I think a lot of them are good. Marsee comes up quite a bit when talking about tank bags. I like the ones that have a shoulder strap attachment. Especially when I have camera gear with. It's much easier getting around with a backpack, and a helmet then carrying both.
Since I use the bag for other things besides gear at the same time. I have placed foam on the bottom of the bag, and use lens wraps on the gear. If I was only going to carry camera gear. I would source foam, either blank or square cut pull outs and make slots for the gear.
Should be able to source foam easily. I use the same kind of foam that Zero Halliburton cases use. Most major photo gear places should have or know where to get that type of foam. Like Calumet, or B&H would be a good bet. Some luggage places that sell any Zero Halliburton stuff may also have sources.
I have a Givi Voyager Bag. I like it a lot. Stays on fine with just the magnets, converts to a backpack and has side pockets that lenses will fit into also.
Inside of Zero Halliburton Photo case.
I carry photo equipment on my bikes a lot. Load whatever I'm gonna use in an old Domke bag and drop that in the tank bag. Never had a problem with any of it. (Couple of times I've carried lights in the Viffer hard bags too, but that doesn't apply here.)