We have just spent our 4th year snow birding in our 2012 Bighorn 3070RL, we have the factory installed slide toppers, I like the fact that they keep rain and other stuff off the top of the slide so you can just bring them in without climbing on the roof if need be. But they do require additional cleaning, the tops and underneath, we had pollen on both sides this year. You do have to wipe the tops of the slides after 3 or 4 months due to a build up of dirt and pollen on top of the slides even with the slide out awning. You definitely don't want to bring all the dirt and pollen into the trailer, the gaskets will clean some off but not all. So as you see they aren't completely work free. I use and extendable auto washing mop to clean off the tops of the slides which requires at least a 6 Ft. ladder of some type, I use a 6 ft. stop ladder.
Right now my bedroom slide top bulb gasket has come out of the track it is attached to and of course it is in the center - I haven't figured out how to get to it so that I can put it back into the track, the awning prevents me from doing it from the roof and my arms aren't long enough to get to it from the side. So it appears I have another task to figure out.
I don't know if you can specify the type of awning material but "Sunbrella" brand doesn't fade and lasts forever - if you can afford it