Grazza,
Change any / all lights in the camper ( not your tail lights) to LED's, worth the effort for better lighting, less current draw.
Strips of LED's in clear plastic tubing work a treat, just seal them in with a little silicone at each end, drill through the tube and silicon then wire or thread a hook onto them - Or Velcro them where you want them around your camper /annex
Make up a distribution box ( pic attached, its an electrical box, got it from a tame Sparky ) to run the lights off, hang/place it where you need it and run your LEDs out from there. Saves having a tangle of wires all over the place. Mine has 5 mts of cable on it, red/green LED, fused and on/off switch - took about an hour to make up.
Distribution Box is also handy when you need to shift the Fridge / TV / Radio / whatever out into the annex or outside or run a spot light / work light around or under your vehicle and trailer for breakdowns etc.
Then run a cable to the farthest corner of your trailer from your battery box so that you can plug the Distribution box into there for extra distance, Oh and put a plug for it in your vehicle, under the bonnet is real handy
Found it to be really useful little setup
Cheers