There are generally two ways to make it: Fixed panels on the roof, the more, the better, or active sun-tracking device. Latter sounds more suitable for a vehicle because less weight combined with limited size makes a better compromise. It gives more output power with less weight to carry around. It also works better in the high north.
One panel weighs around 25 pounds (11.5kg) and gives out max 150W. My test set is drawn on short Ford Transit high roof. Size of the flat area on the roof is 56.7” width 96.06” length (144cm x 244cm). After some study, it seems like flex panels should not be used. They have all sorts of problems - cracking, going milky and losing power to mention a few. Some just quit early, after two years. History draws a picture of not too many happy owners. With common sense, it seems quite apparent plastic will not survive in direct sunlight, and those things are almost all plastic.
Vehicle support is bolted inside the van, utilizing existing ribs. Only holes in chassis are for bolts and wires.
In the given area, I can almost fit four panels, so I compromised to install four. Nominal output is max. 600W.
If cells can be pointed directly at the sun (90°), it increases output around 30-35%, meaning more power with less surface, in comparison to fixed cells. Directing is mechanically complex and creates multiple potential points of failure.
The rotator is Lazy Suzan aluminum bearing, size 20” (50 cm) model ht1582. It should be able to take more than 220 pounds (100kg). The whole set with panels weighs around 123 pounds (56kg). Gears are laser cut from 2mm and 4mm aluminum. Square tube structure is 20x40x1.5mm aluminum, that should be riveted together with supports. Welding is an option, but rivets are sturdier but also making possible fixing easier.
The linear actuator is cheap Chinese 29.5” (75cm) 12V from eBay. It should be able to lift 600 pounds.
Rotator motor is TsinyMotor worm gear 12V.
I used in the design only components available on eBay, but I have no info on how they fit the purpose. I ordered samples and make a test rig when they arrive. Possible problems rise with time and weather.
Price for the whole set should be below $1000.