Rack on fiberglass topper

I'm thinking if getting a topper for my pickup but want the option of being able to put my kayak on top if I don't or can't take the trailer. I would make some aluminum cross bars that would secure to the sides. Does this pose a load problem? What am I not asking about this that I should?

They sell versions with channels compatible with Thule or Yakima towers.

Just know what you're drilling your mounting holes into if you're mounting a rack that isn't there already.  For my bed topper there is a thicker section throughout most of the roof on the inside of the topper.  I needed to drill on the outsides of that thicker section because it is made of a weaker, honeycomb-like material.  If I tried to mount the anchors in that section of the roof I may have experienced a failure of my rack system and the roof of my topper at the same time. 

If your talking about a canapy for your truck they make wood racks that sit between the cap and bed and rise up the outside corners of the cap like an external roll cage and usauly come forward over the cab.

I have modified my last two truck canopies buy putting racks on them for my Outback.  I have yet to have a single problem with them.

I have modified my last two truck canopies buy putting racks on them for my Outback.  I have yet to have a single problem with them.

Same here, I have the yakima track kit installed on top of my A.R.E canopy, both an outback and a T13 up there with no problems.

If your talking about a canapy for your truck they make wood racks that sit between the cap and bed and rise up the outside corners of the cap like an external roll cage and usauly come forward over the cab.

To clarify its a metal rack for hauling lumbar