Mounting rack to shell

I picked up a good used smittybuilt rack on Craigslist and wanted to mount it to the shell. I'd like to keep it as low as possible so I built some brackets to mount it directly to the shell rather than on top of rails and crossbars. The mounting point for the brackets are wider on the rack than the plywood bracing on the underside of the shell. I don't plan on carrying much weight mostly just to mount my awning. Anyone see problems with this mount or should I build a crossbar to out the mounts over the plywood bracing.

 

Are you sure it's "plywood bracing on the underside of the shell"? Most modern shells use a honeycomb type material made of basically cardboard (you definitely don't want to mount anything to that if it is present as it'll compress). My totally unscientific, non-engineering and without having actually seen it guess is that yes, the fiberglass will end up cracking under those small feet from vibration. You need to distibuted the weight as much as you can which is one reason why the rails work well. You may get away with using some large backing plates inside the camper but I'd put larger feet/pads on the rack part as well. I seriously doubt plain washers or even fender washers will keep it from cracking. Even without anything on it, it's going to vibrate and any flex in the shell will probably allow small cracks to start in the gel coating. Of course I could be completely wrong.

Helpful tips: Use 3M marine sealant instead of silicon in the holes; it'll seal better and allow you to reapply if you ever need to. Use nylock nuts, acorn nuts or some other form of rounded/protected ends/something on the mounting bolts to avoid gouging your head when climbing inside.