I wouldn't bother with less than 100 watts of solar. As for what size charge controller you'll ultimately need, that will depend on the roof-top real estate you'll have available on the future camper. Solar panels aren't small. A 140w Kyocera runs about 2' x 5':
http://www.solar-electric.com/solar...fbs-140-watt-polycrystalline-solar-panel.html
So how many will you ultimately end up with?
For speccing out a complete setup, take look at what is included in a kit:
http://www.solar-electric.com/solar-panels-mounts-kits-accessories/prsy/rvandsmbasoc.html
Speccing out a system for a mobile setup is done a bit differently than speccing out a system for a fixed location, such as a cabin or a house.
First, what is the available space for solar mounting? That will determine what is the max wattage you can fit.
Once you know that, you'll know what size charge controller you'll need.
The wattage, combined with your location (hours of good sun per day) will tell you your expected daily harvest.
Then, what size battery do you need to store that harvested energy? If you want long life from the battery, don't drain it below 50%, so whatever your expected daily harvest is, double that to get the minimum battery size you'll need.
Once you know what your battery size is, then 50% of that will be your daily energy budget.
For speccing out a system for a fixed location, you work it from the other direction:
Start with the loads you need to supply to figure out your daily energy budget.
That tells you what size battery you need.
That, combined with location, tells you what size solar array you need to recharge that battery in a single day.