A problem with solar for charging is it means sitting around for 3-4 hours and making sure the battery pack and panels do not walk off. Either a DC to DC charger plugged into the car or truck or taking along a long extension cord and plugging into 120VAC are the most realistic options.
E-bikes are fine for use with an RV or when using a home base, but for camping I would use either a human powered bike or a gas powered motorcycle. The advantage of an RV (motorhome, van, trailer, slide-in camper) is that the solar panels can be mounted on the roof and the battery can be recharged while inside the RV.