I have gone down this road a couple of times for different reasons and here is what I found:
A) Needed a way when bicycling long distances to charge a cell phone and some camera batteries. Found a really nice system that you could put the panel (about 8 inches by 12 inches) behind your seat on top of your tent or sleeping bag to do it. Only issue was it was SLOW and EXPENSIVE. They also make a similar one for hiking.
B) Needed a way to charge camera batteries, cell phone and computer when driving. Found a nice 75W inverter that plugs into the lighter for this. Then I inherited a 300W and mounted that in the front of the truck so I can plug all my chargers in when driving (not at the same time). I now use the 75W in the camper when I need to charge something small like my cell phone and do the rest when driving.
C) Wanted to charge some RC batteries when parked and found a nice setup a guy built with a smaller solar panel. Biggest drawback was the time it took, was great for maintaining but slow for charging.
If you are moving during the day I would go with the inverter in the cab. If not I would put a larger panel on the roof that would give you lots of power instead of the smaller ones and then just use your standard chargers from home.
