Picked up a similar 3 wheeled cart last week (10 bucks at Goodwill, almost perfect), and I have my bag strapped in at the bottom, and an 18 pack cooler bungied on top. For now, it's good, but I'm going to see about adding a bracket at the bottom for a storage box and mounting the bag up a little higher. Might add a bracket for the upper cooler so it's not being cinched down by bungies.
I'm also thinking about a cheaper bag (I have a Grip A, thinking about a Magellan) that I can perma-mount with two plates and brackets. I'd have to add some support for the inferior bag, but once it's mounted, the wear should be minimal.