most of Manx were 'smugglers' - see http://www.ee.surrey.ac.uk/Contrib/manx/catalog/b166.htm
and also
http://www.ee.surrey.ac.uk/Contrib/manx/history/1792/index.htm (esp appendices C50 onwards) - Port Erin seemed to be main site post 1765

stuff wasnt usually kept close to shore line as too obvious for excise men to search