Round or octagonal windows that open

I had been hoping to have a round or octagonal window in my trailer. House windows are too thick for my 3/4" walls. I haven't come across round or octagonal RV windows -- do such things exist?
Making my own would be pretty easy if I didn't want them to open, but I am a little nervous about introducing new potential areas of leakage.
I have seen pictures of numerous trailers with round windows, but I am not sure if they open.
So where does one get windows of this nature? Or is making custom ones the only way to do it?
Making my own would be pretty easy if I didn't want them to open, but I am a little nervous about introducing new potential areas of leakage.
I have seen pictures of numerous trailers with round windows, but I am not sure if they open.
So where does one get windows of this nature? Or is making custom ones the only way to do it?