Didn't season mine . . . just used it . . . No problems.
Its not like a canvas tent (which you DO need to season , I can ASSURE you of that
), the SC bags have a lining in them. NEVER had ANY water in it.
I do use bags up there (suitcases or sports bags) , but I have put things like sleeping bags , pillows , blankets , even Xmas presents , and No water problem.
(I WOULD bag em up though for safety sake , even those cheapo red, white and blue bags).