Battery Storage between trips

Use a disconnect switch or unhook a battery cable.

Consider a 30 to 40 watt solar panel and a controller. That will keep the batteries charged between trips.

3-4 weeks I would just disconnect a cable or use a switch. If you get distracted after 3-4 months they may need plugged in for a few hours.

put a cut off switch right at the battery. you should fully charge before each trip.remember to check water level few times a year a little maintance on the battery will give it a long life

New member after 17 years, wow. I agree with the other answers.

^These are options, but OP explain your situation better.
Stored with shore power, no power, solar?
I never disconnect my boat or camper batteries for storage. But they sit on maintainers.

IF camper has parasitic loads then disconnecting will make the charge last longer, so a disconnect switch (disconnect the positive from the battery to the camper) will help, but even then batteries will lose charge just sitting. You should always keep a trickle charger on it. Typically they hold at about 13.6 volts and this is not enough to over-charge the batts and is fine to just leave on all the time. A smarter charger will monitor the condition of the battery and charge as needed.
Unless you have cold winters where you will no be using the camper there is no need to take batteries out.
Ways to trickle charge:
Solar is the favorite of many. You need a few hours of sunlight to help the batteries - not every day all day for just trickle, but several hours per week. You can get a small portable panel or attach a small panel on the roof, or just take the plunge and get a full solar system (200 watts or more). The charge controllers will do an excellent job keeping your batts topped off. MPPT controllers are the favorites of most ppl here.
or
$12 plug-in trickle charger. This is about the size of a deck of cards and comes with alagator clips to attach to the battery, or you can hard-wire it in and plug in as needed. You need to have access to plug it in, but if you have shore power then likely your camper's Dc power/charger will do just fine keeping batts topped off, however, the $12 charger will do it without constantly using your much much more expensive onboard charger all the time.

I had a small 5W solar panel. It was enough to keep a trickle charge on the battery. I believe it was around 500mA.
But as was said a larger one would be good.
In fact you can get a 200W solar kit for around $250-300 off Amazon.

Andyj suggestion to just take the solar plunge is the easy route after installation but I’d say 300 watts.

2oldman wrote:
New member after 17 years, wow. I agree with the other answers.

Could be a recent name change or something reset the post count to zero.