It will be unbearably HOT and it does not cool down at night. There are a few spots with shade, but in most your rig will not be in the shade. You will need to either be in the water or in air conditioned rig. The SP has electric hookups, but your ac will need to run 24/7. The heat index is very high so you can burn in 10 minutes in the sun, so lots of sunscreen is needed. I would never go there in the summer, but many people do.

It is hot in the summer! Best RV spots (with shade and if you can get them) at Buckskin is spots 66, 67, and 68. Those spots also have full hook-ups. Here is a map https://arizona-content.usedirect.com/storage/gallery/0004/0014/B2114E09034743C9953E010E96A308D2/BUMO_ParkMap_Spring_2019_FINAL_01.pdf