Felicia estate roof rails

Hi

I have a couple of roof rail questions:

I've just taken the roof rails off the old Felicia estate but they're not really much use. My other car has a set and there's not much to go wrong with them so a spare set's probably not worthwhile. I can't see them being any use to anyone else either as they seem to attach to captive nuts inside the roof which wouldn't be there on a car without rails already. Is there a way to remove the captive fitting from inside the roof? (So that there's all the parts to fit to a non roof rail car.)

I've been carrying a canoe on the rails and they take the weight ok but having seen how they're attached I wonder if they are really up to taking the possible uplift from the wind getting under the boat at speed. Do you think I should tie it down to the car instead of just to the rails?

Thanks