In my opinion the Keukenhof is overrated and far too touristic. In that area there are however a dozen nice campsites with view of the dunes, for instance near Lisse and Noordijkerhout. All at biking distance from the Keukenhof. As said above, avoid the Easter crowds.
Tip: in april and may, when the bulbs flower, just take your bike and drive around the big bulb fields of the farmers in that region. Free view of beautiful miles of colors.
Some forty kilometers north of Amsterdam, around the towns of Limmen, Egmond aan Zee and Heiloo, you find similar beautiful colored bulb fields, with dozens of biking routes. Less crowded. Still more north there are flower fields from farmers around Schagen, Callantsoog and Wieringermeer. Again, lots of campings.
In Limmen you find the Hortus Bulborum, a flower bulb garden with four thousand different species. I like it far more than the Keukenhof. Entrance is 5 euro per person.
Hortus Bulborum in Limmen.
If you use the (paid) camping app from Archies, you'll find all the campsites of Europe, including Holland. Or visit campercontact.com to see all the camper places in Holland (and Europe).
Regards from Amsterdam,
Marc.