Visit https://secure.rzda.net/sfwmd/list.cfm and apply for a special use license. :) Easy process.

Try https://www.sfwmd.gov/recreation-site/dupuis-management-area. Apply for a free permit. FYI. They will give you the combination for the padlock. Dial it. Then push up on the lock and then pull down to open.

https://secure.rzda.net/sfwmd/list.cfm Select DuPuis and select your unit type (RV, camper, etc).

I see some great folks already answered! This is my favorite free campground in Florida so far-enjoy your stay!!