Yes, they allow RV's to overnight.
No, they don't charge.
Some have areas in the main parking lot for RV's, others you just park with the Big trucks.
Generally, they are all very noisy no matter where you are parked. Personally the noise doesn't bother me because it's not unlike a lot of campgrounds that have a railroad track running past.
Never been Pecos or Lubbock but did try to stay in Amarillo once. It was a very small Flying J compared to most and not much room for Trucks let alone RV's. I went down the street a ways a stayed at WalMart. WalMarts are much quieter.
Joy A. & Olive
and "Puff", too