Cutting holes in the top of a fiberglass box?

[unlearned_one]

I'm interested in building a vehicle based on a Ford Transit cutaway.

The panels from Total Composites or AdventureTrucks both seem very nice, but I was thinking at the moment of ordering a Unicell Aerocell, since the dimensions are approximate in-line with what I'm looking and that might be simpler.

One thing (among many tbh) that I don't understand very well is how stress affects the roof with fiberglass.
In particular, how cutting holes in the roof affects the structural integrity, and how (if possible) to mitigate that.

With a traditional metal roof, I understand how to build a reinforcing frame, and attack it to the struts.

With fiberglass however, it seems like the sides are "pulling" on the roof to a degree, rather than the roof resting on them.
Are there guides on how to re-enforce this? Is it inadvisable?
I'm interested in any resources that may be available for reading more on this subject.

Thanks!
(And I apologize if I posted in the wrong sub-forum. Please feel free to move if appropriate)

 

[OverlandNA]

I would talk to the manufacturers as they should know their products best.

 

[simple]

Speaking with the manufacturer is a great place start. Cutting holes is a pretty vague statement. They will need to know exactly what you intend to do. Are you thinking of a roof vent or something larger? most likely they will say it voids the warranty or you may need to have them add reinforcement at the time of manufacture. Bonding or laying additional glass and other materials post cure is never as strong as if its done in the initial layup.

A general rule of thumb on composites is that a round hole will have a lower stress concentration than a square hole with sharp corners. The middle of a panel will have the least amount of support and have the largest deflection from loading and wind turbulence. Small holes for fasteners are usually not a big deal but you wouldn't want the holes to close together. Depending on the loading of whatever you are attaching, you may consider sandwiching the fiberglass with plates bonded to both sides to spread the stress from the bolt head out a bit. Think snowshoe.