That is a fairly large TT and those extenders are not intended to be used for a unit like yours. They have one with a 6500lb load capacity using a WD hitch (which would probably mean 600lb tongue weight) and the one to which you refer is 300lb tongue 3500lb max load extending the hitch out that far maybe less to be real safe.
IMO DO NOT DO IT.
Do it the old fashioned way of loading the cart then hook up and if the golf cart does not fit with the tailgate up you have the wrong truck for this purpose.And from what I found your trailer has a tongue weight of abt 840lbs and GVWR somewhere around 9k.
John & Deb
2011 F250 Lariat FX4 Crew Cab 6.2
2011 Flagstaff V-Lite 30WRLS
Days Camped 2013: 16 2014: 5 2015: 3