Probably the best idea is to not pass the caravan plug end through the reel. There is a capture hook in the belly of the reel itself and it is always advised that no cable should be left on the reel when in use.
Therefore, take the cable completely off the reel and use the internal hook to capture the cable end when winding back in. There's loads of space on the reel for a 25 metre cable anyway.
Randa