Ladder Rack Advice

[anotherjoe]

Im building a rack that will mount to the top of my fiberglass cap, it will have an internal frame for additional support. So the rack and internal frame would have a "sandwich plate" with matching hole patterns so that they will bolt to each other through the fiberglass cap. What I cant decide is, would it be better to just drill the cap and bolt through? Im thinking that may risk cracking the fiberglass but at the same time that amount of force dispersed between two pieces of 1.5 inch flat bar might be fine. Or should I add sleeves that are the exact thickness of the fiberglass so that it can be tight but not apply to much force to the fiberglass.

thanks

 

[rockettgpw]

Dad has a Subaru Brumby (Brat) that was fitted with a full length basket rack mounted how you are doing yours.
It was on a single skin F/G canopy. It only had the sandwich plates above and below with a 1/8" insertion rubber gasket either side,May have used nylocs to keep tension.
The rack had only one hole at each mount.
When we removed the rack there were no cracks in the F/G, but it seems that movement in the internal racks had cracked the floor of the brumby. The racks were not braced. After we removed the rack, we filled the holes with chrome bumper bolts.

If the bolts are going through a boxed section of the roof I think sleeves a little shorter than the section wood be a good thing to provide a bit of tension.