I'm so sorry to hear that Ed. We got back from that site yesterday morning, it was very muddy and the cars had churned it all up. The lake was as high as I've seen it but there was no problem on the hard standings.
It may be worth keeping an eye on this flood watch site before you make a final decision
http://www.environment-agency.gov.uk/subjects/flood/floodwarning/011FWFNC6A
My OH says that although the last date mentioed is Jan 2008, there is a date at top left saying Sept 2nd so it could be up to date.
It may be worth phoning the number on that page to check. Maybe the wardens are just being over cautious because the river is high.
I don't know what we would do in this situation but good luck anyway.
Have you tried Castlerigg caravan and camping park? Not quite as handy for the town but you can walk from there. We've done it many times.