Hi Steve
There are alternatives to connecting the panel to your battery via the battery hatch although there should be a slot in the bottom of the door which normally accommodates the ehu cable.
A simple method would be to connect a + and - to the battery using multi strand auto cable of an appropriate gauge and to wire these to a small connector socket which could be run to the outside via the gas locker for convenience.
If you really want to be able to use your solar panel without having to unpack it or lug it around inside the caravan you could mount it semi-permanently on the roof of the caravan and hard wire it into the caravan charging circuit. The solar panel keeps the leisure battery topped up and on rallies I am able to forget about it.
I roof mounted my 80 watt panel,
Click Here to see a step by step guide on how I did it