Is overnight RV parking still allowed?

It must be, because I see RVS there all the time. Trackers and Trailers are not allowed. Unless it's making a delivery to Walmart.

Yes, we stay here often on our way through.

Yes it is

There are signs saying no overnight parking. Every Walmart has one, but very few enforce it. Tractor trailers park there at night. Keep a receipt for something you purchased that day; park far away from the store, and don't take up excessive spaces or block an entrance.