Looks like this is the one you have:
Action Trucks has the Action Contour 3 fiberglass truck cap. Choose from the best truck caps or truck canopies at Action. Shop now.
www.actiontrucks.com
If I were you I would contact Action Trucks to ask about roof loads. Make sure you specifically ask about on and off-road load limits. It looks like some models have the ability to hold a rack, but I'm not sure about the Contour 3 that you have. The roof may look very stiff, but fibreglass is notorious for cracking. To give you a parallel, the Jeep JK/JL roof is fibreglass, and that is reason that the majority of roof racks either require a backbone (i.e. a metal substructure going into the body tub, like the Rhino Rack, that is under the roof to support the roof rack) or bypassing the roof and going straight into the frame (like the Gobi or Kargo racks) -- Fibreglass under a load will stress fracture very quickly. Add corrugations or even typical gravel-travel pot holes (with a lot of vibration and bumps) and it will be even worse. Off road where the vehicle may be thrown off-camber quickly or be jarred suddenly by a ledge makes these forces way stronger. To give an example, there's been a lot of discussion on roof loads in the Australian 4x4 community lately -- one major rack manufacturer (Rhino) reduces their roof loads by 2/3 when off road (So their 75kg rack can only hold 25kgs when off-pavement)(I may not be exactly right on the numbers there but it is a significant reduction). A failure of a roof rack is one of the more dangerous incidents that can happen -- especially in traffic.
