DIY Dually for John Deere Gator XUV

[owlbandits]

I'm looking to find a way to add a second set of wheels to the back of the Gator. (partially for looks and partially for a little extra traction). I've ran through a few options including making a longer axel and threading the ends on the lathe but fear that that plan does not connect the wheels together (ie no added traction and potential for outside wheels to not spin). I've considered gluing/screwing the wheels together but am now contemplating just adding a coupler between the original wheel/axel and a new wheel/ axel in hopes that I can tighten the two wheels together enough. I've attached a picture of my plan. Any obvious flaws I might be overlooking or has anyone done this before in an easier way?

Thanks,