It has rained twice, hard, and no leaks!!!
However, The bed of the truck produces more base than my sub woofer. I can bang on the middle of the bed with my hand and get a rather loud, deep, base note. It makes that note every bump I hit! Even a crack in the road.
First thing I tried was insulation and carpet. That attenuated the noise a bit. The second thing was to put some rubber between the frame and bed. That also helped. The bed was mounted directly to the frame, now it has 1/4" of rubber there. I can stand it now, however I want to do better.
I am wondering what to do next? I think at this point I need to weld-in another cross brace in the center of the bed or use some peel and stick sound deadening material, maybe both?
I found that the roofing material works good but will stink you out of your rig in warm weather. I think I could slap it under the bed and not have that issue. I wouldn't use it inside.