David,
Your question can only be constructively answered if we know more of your needs. It is possible to cope with a battery without support but it all depends on the requirements you have.
First you need to address what you want the electricity for and this I suggest changes very much with time of the year.
Lets throw some general but realistic figures about.
You say DA ing so I assume its a friday late afternoon to sunday afternoon, from April. So its two evenings of lights, say in all 8 hours with 30 watts of lights at the most. [ 8x30=240 watts , = 20 Ah for that]. The pump usage will be low 15 minutes at 6 amps= 1.5 Ah.
The devastating contribution will be a TV or car derived radio. Budget this to be 4 Ah for each hour of use for a modest 18" set and even more if you have a stand alone DVD player as well. For a radio use a portable one if you need it on for long periods they use far less power than a car one and the power come from its own battery.
Lets say you have 3 hours of TV over the week end. It should be warm enough that blown heating will not be needed, convection ought to be adequate other than for a 15 minute fan burst after stand out in the cold socialising.
So we are talking of circa sub 40 Ah for a DA meet.
You should aim not to deplete your battery below 50% [ if your thinking 5 plus years from it, if not abuse it a bit more but never below 25%]. So an 80 Ah battery well charged before the meet is just about adequate. You need a bit of contingency if you need the mover to put the van to bed after the meet. On road you will get some but DA meets tend to be local so the time to recover is limited. Say you need the mover for 5 minutes actually working, it will pull about 60 amps if its hard going so there is another 5Ah that ought to be budgeted for.
So this leaves us with a 45 Ah demand so a 100 Ah battery if your looking after your battery.
I have these days a very power hungry van and I now go away for weeks rather than days. I compliment my battery with a 85 Watt solar cell, but for years I week-ended without anything but the battery. In the winter I use a second battery carried in the car and charged via an inverter and C-tek charger, but for Da meets you dont need this level of complexity.
Cheers John
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