Take one interior light with a fluorescent tube: Gut it and bin the internals: Buy a couple of 12V LED strips off eBay or from Maplin etc: Attach LED strips to lights base with cable ties or strong glue: Join both +ve's and both -ve's on the LED together and wire to the switch (you did keep the switch didn't you?): Revel in the glow of the new bright LED lights. Fluorescent tube: LED: As LED's use just a 10th of the power of a fluorescent tube your leisure battery will last longer too. ;D
Typing in 12V LED strip in eBay brings up hundreds. They are available in red, blue, green and yellow aswell as white and blue/white so you can choose to make your camper look like a tarts boudoir if you want. ;D
That's just what I did, works wonders nice and bright, just replaced my festoon bulbs in my pick up with led ones they are so bright.
excellent guide there mate - Joker has used the very same to illuminate his engine bay (inspired me to do the same) and was wondering about some bright ambent lighting in the van too - these babies are super bright!!