At 5'11 I've always found I band my knees on things in the Falcon's. Also, Ford have always gone for the wrap around feel on the interior so you get the impression you're embedded inside the vehicle. Those 2 points seem to be related. Holden's tend feel roomier cos of that.
If you're towing you want a trailer with an axle set towards the rear otherwise you can occasionally have problems with the back end going light when the weight on the trailer transfers backwards.
Nothing wrong with the Jap utes but the Holden has always been the most comfortable for me. Main thing when you want to carry a bike is the Holden tends to be lower in general than the Jap utes, making loading a bike easier/safer.
My brother has one with a hard cover over the tray. Way more useful than uncovered and removing it is a 2 minute job, although a 2 person one.
Big problem for you is likely to be that the GS is longer than the tray of whatever vehicle you're looking at so the back wheel may not even sit on the tail gate because, as you say, the tray extends under the back of the cabin.
Personally, I've never liked autos. They have higher maintenance costs and require maintenance more frequently.
Zen wisdom: No matter what happens, somebody will find a way to take it too seriously. - obviously had KB in mind when he came up with that gem
Artificial intelligence is no match for natural stupidity
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