Nick I realise you're trying to be a law abiding upstanding citizen but you really can bend the rules a tad when getting your boat ready down there. I personally turn up, pull over in the main car park. Get everything ready. When ready I drive over to the slip, in the centre of the road, until the wheels of the trailer have passed the metal strip that goes over the road. This I have find gives me the best position and amount of space to be able to reverse easily. If the gate is open I simply pop in my 2.50, open it, reverse, put the boat in, tie it alongside the slip, drive the car to the top, turn left, go through the "no entry" signs, stop in front of the trailer park, park trailer, then either park behind the fish market, or take the car home and walk back depending on how long I'm going to out in the boat. I leave the gate open in the hope that it is still open when I come back. Even if someone has closed it the fishermen often open it again.
Conclusion: By not buying a parking ticket for my car and trailer while I'm getting ready, parking behind the fish market, and then leaving the gate open, a session at the camber typically costs me either nothing or £2.50. I have used the slip three times today for various ribs, and it cost me nothing. You can get a permit to park down there but you need to be a resident. Alternatively ask a member of the sailing club if they can get you a couple of day permits at £1.50 a pop.