They work best if they directly face the sun. Most installations on RVs are flat so they are not the most efficient and sacrifice some capacity. Camping in the desert for extended periods many Rvers can adjust the angle of the solar panel to get higher efficiency. The panel would have to actually track the sun's movement to be optimum. Five solar panels can provide up to 25 amps of charging capacity.
Many campers report effective use of solar panels even in cloudy environments.
Wind Mills in miniature can be raised above the RV and if there's a good wind can also generate a few amps of charging capability. They are a pain to put up and take down so are most useful when camped in one place for many days. Generators that operate on gas, propane, or diesel fuel are used when shore power is not available. A typical RV mounted generator has the capacity of 3500 watts or enough capacity to operate a microwave, toaster, hair dryer and color TV at the same time. If all you want to do is recharge the house batteries you could use a portable 500 watt generator powering a 40 amp multi-stage charger and run it a few hours per day when the noise does not bother people.