I just got done doing this for my single family residence. It only cost around 500 dollars (I'm sure a park will be more). And dealing with the engineer and FEMA is a total pain but it was definitely worth it. My home was removed from the 100 year flood plain and I was refunded the amount required for flood insurance. Before I even bothered, I spoke to the county to determine the BFE for my area. Then looked at the basic survey and saw that I was well above this and that I would most likely win.