One of the unusual plans I have for this teardrop is to mount a roof tent on it. With two sleepers, you could be pushing 500lbs including tent and rack weight. So I came up with this - hopefully - sufficient weight bearing solution.
In short, I made three double spars with roughly 5x5 screw pads. I then notched the sidewalls so the load would be transferred into the solid sidewall. The notches were imperfect, so I used nasty liquid nails and, of course, more pocket screws. The space in between the spars is about 13.5 inches. Eventually I am going to use threaded galvanized pipe to make the three crossbars of the rack. I might add some little brackets on the inside under the screw pads.