We asked at the customer service desk if overnight RV parking was allowed, and were told that the company does not allow it, no. But another employee overheard us and said that actually if we park in the far corner and we're out by 6am then it's ok. So we gave that a go, and it was fine.
There was at least one other guy sleeping in his car near us, and in the late evening a ginormous Super C (size of a semi) towing a vehicle pulled in and also stayed the night.
We had every intention of leaving by 6am but it was harder to do than we thought it would be, and it was closer to 8am that we left. I do feel bad about that, even though we were the first of the overnighters to leave.
Had no issues other than standard walmart noise and garbage everywhere. It's near the freeway so it's loud. There's some nice grassy areas for the dogs near the online orders pickup area.
Wifi does reach the lot but it was too weak to be usable for me.