The trussed center is because the center support tabs where not perfectly 90s from the mfg. I bent it as much as I liked and never did removed them to get it close to 90, in fact I like the truss in it now. Not much work. If you buy your Surco supports, make sure they are all the same angle before you mount them.
I never did finish the staining, got lazy, and it's been holding up just well. Of course you can see the weathering the wood has gone through, and in hindsight, I should of used redwood for the whole thing, it's currently spruce and pine, and pine doesn't last very long exposed w/o oil staining.
If you sit your rack on all 3 supports spanning the roof, it will easily support 500lbs. I had about 200lbs sitting on the rear two supports without an issue going up to the Sierras. You can easily sleep 2-3 guys on my roof w/o issues.
I recently had about 322 sq ft of soaking wet carpet on my roof that I had to drive on the freeway for 15miles w/o an issue. Soaking wet carpet is HEAVY!!! No issue

You just need to spread the weight on your roof and you'll be fine.