I had a side window spontaneously shatter a few months ago -- I replaced it with "acrylic sheet", often called plexiglass. I measured the thickness with a caliper and ordered a replacement piece of the same thickness on Amazon,
here. They sell various thicknesses of the acrylic sheet. The first cut was free, and a second cut was only $3. It cost me all of $22 delivered. My window had rounded top corners, so I made a pattern, marked the plexiglass, and radiused the two top corners using my belt sander. Worked great. Installed it, and no problems with it since.
Personally, I would not put auto or any kind of glass in an RV. And I believe OEM "glass" in RV's is generally acrylic sheet.
