How a free port transported seal? (12)
I believe the answer is:
weatherproof
'seal?' is the definition.
(to waterproof something is to seal it)
'how a free port transported' is the wordplay.
'transported' is an anagram indicator.
'how'+'a'+'free'+'port'='howafreeport'
'howafreeport' is an anagram of 'WEATHERPROOF'.
(Other definitions for weatherproof that I've seen before include "resistance to the elements" , "Designed for protection from the elements" , "Resistant to rain, etc" , "prepare for storm" .)