"...Maybe some JB Weld instead..." Not that either. JB Weld is just epoxy glue with powdered metal in it instead of fibreglass.
A Choate shotgun magazine extension is too thin to do much of anything with. They're also shotgun model specific. Existing Choate mag extensions go up to 10 rounds. Knew a guy who had a 30" shotgun with a mag tube that went the whole barrel length. Heavy thing, so it was.