I see what you mean... I'm considering the same thing with mine & I've likely got close to another foot more sticking out the back.
That's really cool! I just wish I was shorter so I could fit better in the Astro.I'm a long time viewer of Expedition Portal. I'm now feeling compelled to share my van. A 2004 Astro with a 4in lift and a freshly installed pop-top off a mid-nineties Aerostar Chinook. I plan to post a formal build thread here eventually once I find some free time. But for now, here's my van after I installed the pop-top.
View attachment 363087