6x9 speaker placement?

[Ironhorse]

Thought I would try this as a post since the search function is still in-op. I have moved my in-cab tank to under the bed which leaves me a big open behind my custom after market seat. Without cutting the lower door panels I am thinking of placing my 150 watt Pioneer tri-axial 6x9's in the cab corners just below the lip of the inner cab pillar. Angled at about a 45 degree at that level. I think that would be a great area to block off and use the cavity as a "sound box". Insulate with some 1/4" foil/bubble wrap maybe? Just not sure how to block it off and have a structurally sound mounting to mount speakers solid. Can't drill holes since the bolts would look rather un-sightly sticking out the side of the truck. LOL Someone had this type of a set-up in truck sometime ago but can't recall who. Anyone know of this or any ideas on how to mount these speakers? Any thoughts or help from the stereo guru's ? Thanks in advance to all who reply.