Electric Generator

How can you make an electric generator?
I own 5 acres of property. Other then my gas generator, I don’t have electricity on it. I have a travel trailer on it with an electric fridge and I love camping there. In Home Depot, I have seen a converter that you hook up to your car battery and I have also seen what appears to be an electric generator. I asked someone at Home Depot how long the “electric generator” would run a small fridge. He told me it wouldn’t be a long time, but suggested using a marine battery with a converer. I am thinking I could purchase several batteries, a converter and a battery charger. Does that sound like somethink that might work?
I do have a 5000 watt gas generator on my property. I just don’t want to have to run it all the time if I am camping for several days or a week at a time. We all know the prices of gas these days.
Sure that will work. With two marine batteries and lights you will have to recharge them about every 2-7 days. You will need to use a gas generator to recharge the batteries. Or you can buy something like a 100 watt solar panel to recharge them.
Most rv’s work like this. If you drive with your camper a lot you might look into running some lines from you main truck battery to your marines so you can charge them all at the same time. But remember to put in a switch to turn it off so you can’t drain all of them and get stuck somewhere.