I wouldn't worry too much about shading from the vents, you can adjust placement before make it permanent. Just take a couple of pieces of cardboard that are about the size of the panels you plan on installing and either watch as the sun goes over the RV or video it. You will need to learn to park so that the sun travels over the rv from the side that minimizes shadows based on placement of the panels. Example if the panels have objects (vents, air conditioner, etc) at the top then you would want to position the RV so the sun goes from side to side. If the shadow objects are on the side of the panel then you'd want to park so the sun goes from front to back of the RV. As for reducing power from shading, yes there will be some but unless the object covers every inch of every panel you will still get power. Some panels do better with shading than others.
Learning to manage the power would be the biggest change like using the high power users during peak hours of solar production (you can monitor that with a good Charge Controller and panel meter) so as to use the solar power instead of battery.
We just bought our RV this year and in the past we did tent camping with solar. I had 300ah of batteries and 420 watts of solar that I just propped up against something with the solar panels pointing south at a 35 degree angle. We had all sorts of devices charging, wife would use a small vacuum to get the sand out of the tent during the peak hours. I used a MPPT charge controller to get the most out of my panels and had them wires in parallel.
I plan on adding solar to my RV as son as I can relocate the batteries to a bigger compartment. Initially I will be using my portable solar panels I used tent camping and place them on the ground, move them as needed. I'll be putting permanent panels on the roof once I have bought all the I need (buying as $$ permit). Right now we are new to RV camping and will be staying at parks that offer shore power.
If you have certain panels in mind I would start by using them on the ground until you are comfortable enough to install them on your roof.
my 2 cents