Snugtop Topper + Roof Top Tent

I haven’t seen how and where these toppers fail but then I haven’t really looked. My suspicion is that it in your case it would tend to be where the load is fastened to the roof and where the topper is fastened to the bed since those are focused stress points. Larger than minimum fasteners combined with larger washers and rubber bushings might both spread the point load and reduce the vibration(think something like the body mount bushings). One other thing I’ve noticed is that the shell mounts tend to loosen. Mine has 6-5/16 x 18 bolts & nuts and that issue was fixed simply by swapping the standard nuts for nylocks. The addition of some rubber washers between the top washers and the shell might help your situation since the underside of the shell already has the bulb seal.
Your going to have more flex and vibration on dirt roads than on pavement and I’m inclined to think that driving stresses are more likely to cause an issue than body weight and snoring.