I have an '86 Westy with the Thule rain gutters. When I bought the car, the
fellow had been routinely carrying 1 or two knacks with no problem. I've
mounted their Adventurer luggage box and only taken a short 2 hr trip so
far with no problems. I'll be adding a bike rack for the 700 mile
pilgrimage to Watkins Glen next weekend. I'll be sure to report any/or no
trouble.

On our '86 Nissan Stanza 4X4 we lost the roof rack at 70 mph in the fast
lane  on I 495.
Imagine how scary it is to look in your rear view mirror and seeing your
rack of camping gear spinning off behind you! The rack spun around and came
to rest on the shoulder.
I use motorcycle tie downs to hold the stuff on the rack and they held the
load together!
Since we packed up the tent in the rain, the failure was probably due to
the extra weight of the water still in the tent.