Bike Rack receiver wiggle

On my Fifth, we had the factory install a hitch, specifically for a bike rack (I already knew from the forums, bumpers were suspect!). After going through all the brands, found that Swagman was about the only game for trailer rated racks.

Leaving in about 3 days, and was finally able to get my new rack (Swagman XC) and the Fifth in the same place. The Swagman is the one that comes with an adaptor for bumper mounting, if desired. No, I didn't use it.

Turns out the receiver is under and behind the bumper. In this configuration, bikes are hitting the rear window of the fifth. So off I went to get a 6" receiver extension.

That gives me good clearance. But, if I lift the whole assembly fast and hard, to simulate going over a bump, there is a pretty large amount of up/down play. I cannot get the handlebars to be less than about 2" from the window, so I'm hoping there won't be any really big bumps in my future. The play seems to be due to the looseness of the rack tube going into the extension, and then additional from the extension into the receiver.

Any suggestions on how to stiffen everything up so there isn't much play? Or am I worrying unnecessarily?