If your only looking for two days, maybe an occassional 3rd day, I would make the investment in a better battery bank first and see how that does for you. Switching to a couple higher group 12v batteries like group 29's or higher or 2-4 6v golf cart batteries will increase your Amp Hours significantly. Switching to LED bulbs in your light fixtures for a couple bucks per bulb will reduce your battery use for lights by about 70%-80%.
Both of these steps would be wise and required as part of upgrading your camper to off grid use for extended timesframes. You may find that doing these Two things gives you plenty to mean your modest needs of only a couple days off the power cord. If not, your ready to do the solar thing and in a much better position to store more energy (bigger AH battery bank) and use less (LED lights).