I have been to Filton quite a lot.
They are very friendly - cost for landing and a days parking around £35. The parking is a reasonably significant addition to the landing fee. In case it is relevant they open at 10-00 on a Sunday (and also on Saturday I think).
Taxis seem easy to get - about 20 miniutes into the centre although I gather it does depend very much on whether or not it is rush hour. Expect much longer in rush hour. There is also a very good bus service from outside the main gates into the centre - every 15 minutes I think.
Filton seem to use their reporting points so check these. There is of course an ILS which they do seem happy to turn on at weekends although the "official" approach services does not seem to be available. Sea fog would seem to be a problem. They are PPR and expect a 'phone call in advance.
Parking is etiher next to the "C" or on the other side in which case it is a pick up in their landrover.
If you are coming form the East Lyneham will give you a LARS but watch as you leave their zone because Colerne like a call and it is easy to infringe their ATZ. You migt be asked to talk to Bristol City as well.
Filton always seems to be very quite - I dont understand why because it is a pleasant place to visit and very convenient for the city.
G-BOAC is there but unfortunately now closed after the sad accident last year.
They prefer you to use the westerly runway (cant remember the heading) so you might find you are offered a tail wind but seem happy if you request the easterly. There is of course "miles" of tarmac!
Enjoy.