ancaster out back of grantham, maybe easier to find ancaster and the air field if ur looking on map websites, also on the high dyke (the long road its on) there is a bloody great big tank outside it on stilts about 10foot in the air, so if u miss that your pretty lost to finding the site, also its the same place as ancaster karting.
http://www.ancasterkarting.co.uk/company/contact_us.html
BE WARNED!! GRANTHAM IS A PIG TO DRIVE AROUND CURRENTLY!! road works all over, new 1 way system so update your sat navs. also the roundabout on the a1 is being dug up!
There is also a proper camping site over the road, a 30second walk if that.. thats a couple of quid for a spot + fresh water etc its alright as simple camp sites go