I am replacing a side window in my burro. There was previously an air conditioner there and the PO took it out and jury-rigged a plexiglas replacement that leaks considerably! After looking at several window sites, I followed the instructions for measuring and removed the inner clamp ring without disturbing the outer window and seal. That allowed me to measure the true rough opening and the thickness. I came up with 24.5 in wide by 19.5 in high, 3 in radius and 1/8 to 3/16in thickness. I am not sure this is the standard opening because it looks like the opening was not factory, but maybe cut out to remove the AC. I ordered a crank-out window from Callen campers in San Diego (El Cajon) for $100 + $25 shipping, custom made to my measurements. It hasn't arrived yet, so I will have more info on installation in future.
After measuring I put back the clamp ring back. It is too wide and not a great fit, but apparently some of the screws were loose before because now it leaks a little bit less!
Thanks for your reply.
I wish I could see the true opening, the PO did a fancy job of replacing all of the windows
with smaller windows
& plywood! He used two pieces which were larger than the opening for each window, screwing them together through the opening, and the opening is supposed to be untouched. He then sealed all of the edges to the fiberglass. Somewhere floating around under there is our window well. I'm hoping we don't have to take it apart to measure, because while the current job is ugly, it's fully functional, no leaks.
I'm about to guess on sizing & order a front window, that's the biggest eyesore, no window, just plywood with a window a/c... but I don't know the wall thickness for the trim ring, the site says it's between 3/8" & 2 1/2", and yours is much thinner. Hmm.
Good luck with your new window! I look forward to seeing your upcoming installation.