Does anyone having experience renting an RV in Kunming? If so, where did you rent from and what was your experience traveling in one?

you might be better off buying one in many ways. I've never heard of any rentals. RVs are still a bit of rarity.. I've seen more van conversions recently... maybe they would be big enough?

I have seen rental RVs parked along Haigeng Daba. Next time I see one I will photo the company logo and send to you. I thing one had Chongqing number plates. You could maybe take the train to Chongqing to collect.
I have also seen RVs parked by the lake management building at the end of Haigeng Park on the corner of Xingti Lu and Hubin Lu. I am not sure if this is sales or rental or both.

There are also RVs parked along the new apt complex behind the Wanda twin towers. If you walk by during daytime, I'm sure you can ask someone who rents them.

I know the people who own the RVs at Wanda and are doing RV projects all around the province. Feel free to PM me if you want to get their contacts.