I just did the opposite of what you want to do. I replaced my fixed rear window with the sliding version. As someone say previously, opening the rear window is a great way to get air espescially if the wind does not blow in the direction of the side windows
. Think twice before replacing that slider with a fixed window.
If you still want to proceed, the sliding window is exactly the same dimension as the fixed one. But the sliding version is sandwiched to the trailer by the window itself and an aluminium molding, btoh of which are held by screws.
The fixed version is held solely but a rubber molding. this molding has a round rubber rod that locks the plexiglass. If you take a good look at the front window, you will understand.
You can get a full kit from Scamp
which are greatly cooperative except that they wont ship anything to Canada bigger than what the postal service will ship.
If you still want to procced, my rubber molding is for sale
for 10.00$. You can contact me at : farfelu47"mediom.com.
By the way, the front window is a bit taller than the rear. I checked.