[EricH]

Originally Posted by Colin P

I thought he meant unsupported sections of bumper as in:

[[[[Bumper]]]]]]]]
I______I_______I <--Bolts to frame
---x---- ---x---- <--distance between bolts
x>=8" ?

He did mean that.

Because that is what was meant, there are two roads to go down, or maybe more. Being off the Frame Perimeter by the width of a bolt head, OK, maybe an inspector will let that slide. The distance between the bolt heads, OK, probably (it won't be measured center-center, BTW). Depth of gap, Probably a pass anyway, considering that most bolt heads are less than 1/4" thick.

But, that being off the Frame Perimeter is the big issue here. The stress concentrators known as bolt heads could be a big issue; if there's a hard enough hit, the plywood could be damaged--nothing like a small object that's harder than you are to break you.

So, my suggestion is to make pockets for the bolt heads, and be unquestionably legal on that front.
__________________
____~______~_____ <--bumper backing with the bolt heads in pockets inside it