To be successful camping off the power grid First you need to reduce your 12VDC power drain everywhere you can. Changing over the ceiling lights to LEDs is a hugh big step here...
Then you need to beef up your trailer with more batteries to run all of the things you want to run running directly from the 12VDC Batteries or from an proper sized INVERTER connected to the battery.
Then you need to come up a successful way to re-charge your battery bank in a quick manner. Changing over to the smart mode charging is the way most folks go. Then you need to learn how to quickly re-charge your battery bank in a quick three hour run time which usually is best to connect your trailer shore power power cable directly to a 2KW generator 120VAC receptacle. Solar Panel will only enhance the charging of your batteries unless you have many many panels. A 120WATT Solar panel will only produce around 5 AMPs of DC current. To re-charge just ONE DEEP CYCLE battery in a quick three hour run time you will need around 14.4VDC at between 17-20AMP DC Current to do this.
You just can't run into the woods with a small solar panel and do much of anything. You will get behind in your battery charge status real quick and if it stays this way for any long period of time it will harm your batteries.
Rule of thumb for long battery life is to always re-charge your deep cycle back up to their 90% charge state when they get drained down to around 50% charge state. Letting them set in a discharged state is very harmful to the life of your deep cycle batteries.
Three 120WATT Solar Panel will give you around 15 AMPS of DC current but only when you are in HIGH SUN. Can't depend on having high SUN when you really need it. Might be a cloudy day. Might be cloudy for a week... This is why you must have the Generator as primary method of charging your batteries. Then the small solar panels can supplement the generator run time and maybe not have to run as much.
Also you have to follow the camp ground generator run time restrictions that may be in place. This is why you want to get re-charged in the three hour generator run time period.
Of course if you just want to be in the woods and run a light for a couple of hours maybe fire up the TV etc then a couple of batteries will work for you. When they get run down however you really need to re-charge time in a timely manner otherwise you batteries will start going bad on you... I give up candles and a bag full of D-CELLS batteries along time ago.
We are just now considering to add SOLAR PANELS to our 255AH Battery Bank setup. We do just about everything we do at an electric site except no air conditioning and can make it through the one day/night run off of the batteries and be right at 50% charge state the next morning. This is when we re-charge the battery bank using smart mode charging techniques being run by the 2KW Generator for three hours. Adding SOLAR PANELS will hopefully reduce the times we need to run the generator. We cannot be successful unless we start each day/night run off the batteries with them charged up at their 90% charge state. NO fun running out of batteries at 10PM at night on the East side of the US.
Lots of things to consider here to be SUCCESSFUL. NOTE I mentioned the word SUCCESSFUL...
It will take some planning and trial runs on what you really want to do when camping off the power grid...
Roy Ken