Super easy. Ive done a few and just did the one on my new Puma. About 90 minutes. Helps with 2 people. As with the poster above. Lots of screws!. I went with a Dometic Slide Topper. My other trailers had this one and worked great so I stuck with them this time around. American RV Company for me had the best price. After having them I would never go without one. Esp with our second trip with the new trailer. I did not have it installed yet and we got a freak snow storm the 1st weekend in May and when I slide the slide out in , a lot of snow was still up there, got under the seal ,melted and completely soaked our new interior floor and carpet....
I basically mount the extension arm brackets up snug into the corners of the slide out flanges. From there I use the directions to measure up from there in order to screw in the long bracket. Once that's done it takes 10 more minutes to slide the topper in place and setup !