I go on C&CC rallies at least twice a month Pete and use a 110 amp/ hour leisure battery.
With judicious use of the 12v systems such as halogen lighting, the water pump etc the battery easily remains charged and usable for the duration of our stay ,usually Friday afternoon until Sunday afternoon. We don't use blow air heating or the OmniVent fan over the oven skylight to conserve battery power.
After gaining more experience of non ehu rallying I've replaced the GU4 halogen reading spots over the headboard and the G4 halogen bulbs in the main 12v lounge lights of our Abbey 620 with LED 'bulbs' from
Ultraleds
These may seem expensive compared to LED's from Hong Kong which are available from EBay but the 'blurb' that I read tells me that the ultraleds have built in resistors and they are suitable for the varying voltages available from caravan leisure batteries.
The leisure battery might hold 13.5 volts at the beginning of the rally and only 12.3 volts at the end.
I also regularly charge both of my leisure batteries (I have a spare)with a C-TEK deep cycle charger to maintain them in good condition.
I might try some of the cheapo EBay LED's as replacements for some of the other halogen spots and the other set of overheads to see how they compare.
Because I now spend so much time 'off ehu' I've bought an 80watt solar panel but I haven't rigged it up properly yet.