Both installed prices seem very high. I've never had a slide topper but I've also never seen the need for one. You could always install it later if you really felt the need.
As for vent covers, absolutely. When it is raining outside, the humidity will be way up and you will need to vent your trailer. The vent covers are perfect for that. If I were to do it over, I would get those Fantastic Ultra Breeze Vent covers as that video Soundguy posted really tells the tale. However I'm am still very satisfied with the MaxxAir vent covers I currently have. They are very easy to install yourself so save your $$$ and do it yourself.
