I had a 30" extension (the largest available at the time) from toyhaulerextensions.com installed on my 2013 Raptor fifth wheel in October 2018. As J Alper stated, it looks like a box bolted to the back of the trailer. I just looked at their website and see that they have revised the design since last year and the new ones more closely meet the roof line and look quite a bit better. Regardless, the functionality is the same. Overall, I have mixed feelings about mine. It accomplished what I needed. I bought a Can Am X3 4 seater and needed to fit it into my trailer's 12 foot garage. It's worked perfectly for that. The kit seems very strong. The back wheels of my Can Am sit fully on the floor of the extensions and I haven't seen any issues with that.
My issue (other than the boxy look) is that I spent the first few weeks after I got the trailer back chasing leaks. I drove from Murrieta all the way to Havasu and stayed the night at a hotel out there to have the install done. When I picked it up, there was some obvious daylight coming in around the ramp door. They stated that the original rubber seal on the ramp door was so flat and worn that it wasn't sealing. When I got home, I got a new seal and took care of that. Within a few days, we had a decent rain. I decided to check the inside of the garage and had a few large puddles in there. Once the rain stopped I did some troubleshooting and found a few places where they did not get a good seal between the extension and the trailer. They seal it with caulk, but I guess they got careless because there were a few spots where I could shine a light through. In addition there were leaks between the side panels and the top panel. The extension is made in 4 boxed sections (top bottom left and right). When they joined the sections together, they again got careless with the sealant. The final issue was that the ramp door still leaked a little with the new seal. The reason for this is that the back of the extension is totally flat above the door. Most toy haulers have a kick out that covers the top edge of the door, so rain is not puddling on top of the ramp door seal. With the extension, that feature was lost. I ended up making my own rain gutter out of a piece of aluminum and placing that right above the ramp door. That took care of the issue.
I made about 8 trips to Glamis last season with the Can Am in the trailer and didn't have any additional issues. The product works for what I need, but I wish it looked a little better (seems the newer model does) and I really wish I didn't have to put so much work into it myself after paying over $6k for it (with install).