Exterior Conduit In Variable Climate

I'm designing a fiber optic PIDS for a correctional application and want to run the backbone cable in conduit on the fence. In the past the client has had a terrible experience with the conduit in use on the site expanding and contracting, as the weather changes from one extreme to the other. I'd like to design this problem out for them.

I believe Fiberglass actually expands more than PVC or coated Steel conduit. Does anyone in the community have a product they like for these kinds of applications?

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