Camping in the Everglades in April

If I remember correctly, the ranger activities wrap up in March, I guess because it gets hot from April on. But now that Flamingo has electric, you can fire up the AC as needed. I sort of doubt you need res then, but you could check online to see if it was filling. There's a marina at Flamingo for launching your kayaks.

My wife and I love the Everglades NP, and the 10,000 Islands
For the Northern Everglades we always stay at Collier Seminole SP
For the southern section we like Flamingo. Flamingo has some sites with electric, but none with water and sewer. There is water where you can fill your on board tank and there is a dump station.
Long Pine Key has sites but without water, elec or sewer.
Also if you want the southern end you can stay in a private place that is nice with full hook-ups in Homestead called Miami-Everglades Campground.
If you want some good places to paddle in the Everglades, check out our google web site at;
https://sites.google.com/site/flkeyskayaktrips/

Make sure to bring a Thermacell with you if you want to sit outside. The no-seeums and mosquitoes can be very bad

If you mean outside the park then Collier-Seminole State Park is the place. They have their own docks in the park and you can launch from there. There are a couple of CG in the park itself in the main section of the park, Long Pine Key Campground and Flamingo Campground. Flamingo has electric and Long Pine has no hookups.