I'm not sure why the previous review said this was closed. I was parked here from Dec 24, 2017 to Jan 1, 2018, and there were other people here, too.
I did get the feeling that this wouldn't be open much longer, since it's surrounded by big malls and constructions sites, but it was open for me. Electricity and water worked at numerous sites (probably not all). Bathroom was marginal, but had flush toilets and cold shower.
I paid 300 pesos for nights when I was there, using electrical and facilities, and 100 pesos to leave vehicle parked there when I wasn't there (no power hookup or facilities). It was a safe place to park, a quiet place to sleep, and a convenient place to stay in Merida. I was happy to have it, and hope to go back again!
Blog: Uphill Zen
Place: Rainbow RV Park
Visited: January 1st, 2018
Location: 21.04167, -89.63028