If it’s the 1140 in your signature, you will need to use molly bolts, well nuts, or other expanding anchors.
The roof is solid...
foam, sandwiched between two thin layers of lauan. Foam doesn't tend to hold screws very well, and the luan is too thin. The expanding anchors and lots of sealant works well.
It's also lacking in the truss department, and completely different construction than their trailer roofs.
If you go up and over the AC unit, you can fit a lot more up there. We have been running with 1800W for nearly 15K miles now, and nothing has budged, loosened, or leaked. As an added benefit, the rack pushes branches and other high debris up and over, rather than wreaking havoc on your roof protrusions. It adds less than an inch to total height, with the AC unit nestled up between the rails, and you can use residential or commercial panels that are both cheaper per watt and if you buy the right panel, have better tolerance to shading.
You should have the cathedral roof on the 2018, but from everything I've seen and read the only thing that changed regarding construction is the shape of the foam block they vacuum the lauan to. This is a cutaway of the roof according to Arctic Fox during an interview with Truck Camper Magazine regarding the change in 2017.