I have never heard of hollapow... I have ridden river ranch, and let me tell you there is a ton of land out there to ride. plenty of water and mud out there. I actually live in frostproof and there are 2 parks that are close to me. Triple Canopy ranch has some serious mud pits and some decent trails. it is just south of River Ranch. There is also Dirty Foot Adventures which is going through some financial things right now. they have a serious mud pit as well. I think you actually have to buy land at River Ranch to ride there. I have been on one of my buddys visitor passes. Here is one of my buddies videos out at river ranch...
http://youtu.be/qCe3qzp9LdM