I often get the questions on how much solar should my van or RV or trailer have. My standard answer is usually not the correct answer. I often say “Get as much as you can afford and fit in your space”
The question should be not about solar panels, but about how much BATTERY should I have. Your whole power system does not run on solar. It runs on battery, when off grid. Solar just recharges the batteries when the sun is out, in which peak sun only averages about 6 hours a day.
So, now I say, “Get as much battery you can afford and fit and size the solar to effectively recharge that battery system. “
Now, none of this can be done intelligently without you first doing a practical power audit. You will have to determine how much power you need in your Van, RV, 5th Wheel, Sail Boat or whatever you need to power.
So, take your largest power consumer. Usually this is refrigeration, which runs 24/7. Get the electrical power rating of that fridge and multiply that by 24 hours in a day. IE, 600 Watts/hour times 24 hours.