There is a caravan site on the access route to stevenston, on the left hand side if you take the road from the R-Bout at the cemetary. I dont know any other details than that, just no it exists - will have a look into it just now though

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<<edit>> found some sites close (ish) to troon and stevenston for camping.
Sandylands Caravan Park (Is the one near stevenston beach)
James Miller Crescent, Auchenharvie Park, Saltcoats, KA21 5JN
0871 664 9767
Cunningham Head Caravan Park
Cunninghamhead Estate Caravan Park
Cunninghamhead Estate
Irvine
Kilmarnock
Ayrshire
KA3 2PE
01294 850 238?
St Meddans Caravan Site
Troon Rd
Loans, Troon, KA10
01292 312 957
All of the above and more can be found
here.