If its South Padre Island, Tx you mean... Yes, we have stayed at the KOA their for a short while. Never long term as I remember it being $50/night.
The KOA is not on the beach if you are into that kind of thing.
2011 Sunseeker 3170DS - 30,000 miles explored
This past October we stayed right on the water at Gulf Waters RV Resort in Port Aransas. Great place with a rating of 10. Not sure of the price but with my Good Sam Discount I think I paid about $60 a night. All cement pads along with a cement table and BBQ at each site. I would stay there again for sure.
South Padre Island KOA is nice but the sites are very close to each other. Depending on your rig, it may be difficult to get in some sites as the roads are very narrow and they have wooden posts between each site. There is also a state park nearby, Isla Blanca with approximately 600 spaces. Also, while you are there check out BadaBing Bagels and Gabriella's Italian Restaurant.