underfloor storage box water
After a tip from a SMB guru, I looked further into the water seepage problem and found out that the box had been improperly installed at the factory. One side was bolted up tight against the bottom of the van and the other side down a good 3/8 of an inch.
This did not allow the sealing gasket to tighten thus allowing outside water and splash to enter around the top fo the box. Also their black sealant was not completely installed around the perimeter. It appears the box was installed in a half #^*'d way. My only choice, short of dropping the entire box down, and starting over was to use silicon sealant, around the entire inside perimeter , and outside on the driver side. This was no easy task working upside down in the box. The problem was so bad and the gaps so large that it took 2 complete caulking tubes of sealant!
Others with this box may want to check their installation, as it will not only be water but also dust seepage to the interior.