Wot size wire for buried cable to 50A RV receptacle at home?

I ran #6 copper through 1-1/2" pvc, 24" deep trench for about 100'. My inspector passed that with flying colors. I ran the wire through each 8' section of pvc and then once all wire was through the pvc, I then glued the pvc ends together one at a time in the trench. Trying to run #6 wire through a already glued pvc would be really, really difficult.

You had better contact your inspector to make absolutely sure on the #8 wire.
Ron