The original Bose speakers in my 03 Touring are about shot. I have a pair of Infinity Ref 6522ex set to install. In looking over some installations posted here, it seems that people simply drill new holes into the plastic door panel to switch from the three-screw Bose to a four-screw replacement. Does the thin plastic really provide sufficient "bite" for the mounting screws? The original three holes all have extra backing for the screws, but only one of those holes can be used with the new speakers. So, do the new mounting holes need to have backing blocks added? Or is it sufficient to just be gentle with screwing into the thin panel?