A quick search on Amazon (where I found that picture), showed a similar rack/platform setup, but it had lower weight limits... Mine has a 500 pound limit before you apply the bike rack. The one I saw on amazon, says its a 300 pound limit for the platform, and 150 or something for the bike attachement.. Although thinking about the specs on the model Y, the Y has a 350 pound tongue weight limit... So I guess the one on Amazon should work for the Y.
Edit: I read the Amazon specs wrong... The 4 bike version has the above specs... The 2 bike one, says 400 and 80 pounds.
​
So the window thing makes sense. I hadn't considered rolling down that rear window.
As far as the bike mount thing, I hadn't considered that and does complicate matters.
If you stargaze on the roof, I'd put a roof basket on and you can build it out as a nest like area.
You could do something like this rack with one of these bars