Thanks. Actually, I think that the silicone stuck, but there must have been more pervasive cracks that I initially saw.

I may try the flame treatment for entertainment, but I now figure that if its cracking now, it'll only get worse and I'll always be looking in the box for leaks, no peace of mind that my stuff in there isn't rusting or mildewing.

I'm strongly looking at either a 46" alum. bed chest, or a 48.5" bed chest. Both would be mounted up in front of the bed and fit between the wheel wells in the bed. I haven't seen a crossover box that fits well locally. The ones that I've seen measure like they'd stick past the outside of the rails a little, and I don't like that look. My rails are ~65.5" wide. Boxes for the Tundra measure wider than that.