It's been a number of years since I've been around that style window, but I believe you do need to unscrew it on the inside of the trailer. I'm pretty sure these aren't clamp style windows, so the inside screen part doesn't act as a clamp to hold the window in. It's just a way to mount the screen and still have it look alright. The little twist tabs are for mounting optional storm windows, but the tabs came on all windows.
I haven't changed a window crank before though (just knobs), so I can't say if the window itself needs to come out in order to remove it from the torque tube for replacement.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR