I bought plastic solar panel mounts similar to the ones Shadow Catcher used. The 160 watt solar panel that will be permanently attached on my roof is about 58" x 26". It will have four corner mounts and two longer air foil mounts in the center of the long side. Using tamper resistant bolts seems wise.
Home Depot now sells a 180 watt Grape Solar for $258.00 that is the same size as the 160 watt Grape Solar panel I bought about a year ago. A 39.5" x 39"
Renogy 150 Watt 12 Volt Monocrystalline Solar Panel that costs $194.45 from Amazon is another higher capacity solar panel that could fit on the roof of many small campers.
There are pluses and minuses for roof mounting a solar panel to your camper. On the plus side there is no ongoing time and effort required to set it up or take the solar panel down to store it overnight. It will harvest power any time its out in the sunlight including while the camper is being towed. Installing a solar panel flat on a roof will often/sometimes not be the optimum angle to the sun. I figure using a higher wattage panel and a MPPT solar charge controller will help optimize the energy harvest. A minus is that camping under the shade which may be desirable on hot days means there is less opportunity to harvest energy to run devices or recharge a battery.
A portable solar panel can be placed in the sun while a camper is shaded. It can also be angled to the sun to maximize the power harvested. There will be ongoing time and effort to set it up, move it around to maximize the power harvested, protect it from theft, and to put it away at night. A portable solar panel will not generate power while you travel during daylight hours.
It is possible to roof mount a solar panel, or several of them, and to use one or more portable panels too for the best of both worlds. It would cost more for the extra solar panels, may require a more expensive higher capacity charge controller, will require more storage space and would add more weight.
There are valid choices and trade offs to consider/decide what's the best or preferred solar power solution we each may decide to use.