I dont have any first hand experience with the G3, but I have had my hands on them. From what i've seen at boat shows and on showroom floors, they seem pretty sturdy. The ones i've seen were fully welded with the aluminum floor. I grabbed the gunwale and tried to flex it in the center of the boat, no give at all. I also believe the sides were double thick (ribs sandwiched between hull and aluminum on the inside. There were other things that impressed me, but i dont remember specifically what they were, as the last time I saw one was probably almost 2 years ago. The polarkraft I have experience with is my uncle's 14' riveted jon boat. Its probably at least 20 years old and has been thru hell. He's duck hunted and fished from this boat since he owned it. Duck hunting around here involves mud and sand bars, breaking ice salt water and sometimes big waves. The boat is still in great shape. The only thing that hasn't held up is the paint in the high traffic arears. Mud, sand and silt being walked on tends to grind paint off. I know this is smaller than what you're looking at, but i imagine they put the same quality into their larger boats.
I think a Polar Kraft is set up better for catfishing than the G3. Polar Kraft has the advantages of a bow mount fuel cell, .125 gauge hull and a large livewell. The G3 is a .100 gauge hull, small livewell, and a rear mount fuel tank.