yeah first of all a 110amp/hr leisure battery is £94 at go outdoors or you could get a 75amp/hr for £60 which if only for running lights will be more than enough, depending on how long your going for, but these will last you more than 2 weeks holidays, the other option would be to buy the same battery as your car takes and then you can swap then around as needed to recharge it
I tested the light setup with a mains to 12V transformer today with the cheapy £3 dimmer I bought on Amazon. Works fine (also has a crazy flashy program that I'll set on my wife when I nip to the loo).