Good morning, Tomtytom
As you mentioned, weight and balance is critical!
But may I suggest you include Shenington Gliding Club on your itenerary? It is 7 nautical miles northwest of Banbury. There is always somebody there who would welcome you, PPR can be accomplished by phoning 01295 688121, or email me a couple of days in advance. There is a clubhouse with showers, loos, BBQs, and sleeping under the wing would raise no eyebrows if that is your plan. And there is a bar, of course.
Just remember that wire launching of gliders takes place, any day weather permitting, and probably even if you radio, nobody will answer, so you must be switched on to observing the runway in use, whether cables are on the ground, or gliders about to launch or to land.