I could be wrong, but I think you have got the parking charges wrong. Surely it is not £10 an hour after 2 hours, but £10 for 24 hours?
As regards the 737-800, the problem is when the runway is wet. CVT ATC are too prone to state that the runway is wet-wet-wet when there is no standing water, but when they state this, the -800 has performance problems at CVT.