I've been using a half decent 70Ah leisure battery, and half decent leisure battery charger at home for a couple of years now. Costs more than an old car battery, but has lasted over 3 years so far, and still going strong as far as I can tell!
I've done 2 day nationals, regionals, and club days on it for the last 3 years, so it's done car and transmitter battery charging, sometimes for more than 1 person, plus the camping with a 240v ac inverter for phone charging, a bit of music and light in the evenings...it's never run flat leaving me short trackside, and I've never had the initial purchase cost, noise, smell, space or petrol running cost problems of a generator!
Leisure batteries are designed for deep discharging so suit our charging and relatively low power situations perfectly...it's what they are designed to do! They have thick plates inside, that don't deliver high power bursts, but degrade very slowly over time.
Car batteries and quite different. They are designed for a single high power burst once every so often, with charging happening in between to keep the voltage up. They have very thin plates inside that will degrade much more quickly if loaded and discharged over long periods. Hence they don't last very long doing deep discharge duties.
If I decided I wanted to run more electric stuff at nationals...I think I'd just buy another leisure and inverter and carry 2! It'd still be less to carry, and cheaper! But your camping...it should be a bit more back to basics