In a camper that is
You will need to find the studs in order to drill for brackets. Since the studs in a camper can be irregular, I would use a stud-finder. Once the brackets are in place, add wood fro shelves.
You can also buy adhesive shelves that are permanent.
There is good information here:
She wants to put up shelves in front of a window inside a camper.
Hopefully the studs on either side of the window’s rough opening go to the top plate in camper framing.
I had an enclosed car trailer that had metal studs and had to use sheet metal screws with pre-drilled holes.
I would drill small exploratory pilot holes, if a stud finder and rapping on the wall (sound detection) with my knuckles, isn’t working.
I would get those floating shelves that hang on a french cleat, or you can make your own cleat from wood if your handy...... https://www.google.com/search?client=opera&q=hanging+floating+shelves+with+french+cleats&sourceid=opera&ie=UTF-8&oe=UTF-8
she wants to put shelves in front of window
If your windows are that tall then you would need ladders and the correct items to install the shelves whether it is concrete, brick or siding or is this inside your home? How would you get to the shelves if they go to the roof?
I would hire someone to install them. That would be the safest way
The windows in the camper go almost to the roof?
If you put shelves in front of the windows, then it may be difficult to open and close the windows.
Please post a picture from inside your camper where you want the shelves, so that we can see exactly what type of space you have to work with.
It depends on what you have to fasten them to, how much space there is above the windows and what you are going to use them for. A few pictures would help. If there is room and enough support, you could attach a shelf with brackets. Good luck and stay safe!
Good luck, camper studs are usually only 2x2s some even 1x2s that won't hold much weight on a shelf, and you will have to be extra careful not to puncture through the stud to the outside metal shell. Then there is the fact you will have to take all the stuff off the shelves everytime you move the camper.