Far as I'm concerned, a roof rack is a waste of weight.  The one that came on my Lance is VERY heavy.  At least the black beams I could remove.  The permanent mounted silver arms are just as worthless and they help trap water on the roof when I have the winter cover on.  
Putting anything on the roof is asking for trouble.  The weight up high is going to cause a lot of sway compared to weight hung down low.  If you can't fit whatever you need inside the camper or truck, then get a small tow trailer.  Putting******on the roof is also going to bite you in the ass when you forget and wipe it off when you don' clear that tree branch some day.