My guess would be the 45 comes from estimating 90 amp hours for a good deep cycle battery but realizing you shouldn't discharge below 50% of that. You want your family to see zero energy remaining on the meter at that point and turn off the TV.
Really 100 watts is nothing in a RV. Sure it will attempt to charge the battery, but your CO meter, propane detector and refrigerator will combined use about 35 amp hours daily
If so, we wouldn't have been able to go four days on 2 batteries (50% discharge) without charging! Our fridge must use less power than that. Or it may be cooler where we camp. No light, no defrost feature, no fan. CO detector runs on a 9 volt battery. I made a few measurements and figure a 100 watt solar panel should let us go without other charging sources for twice as long - a full week. Of course we don't carry a TV and use propane to make coffee.