Do not overestimate Tamron's weather sealing. My recent experience tells that both sealing against dust and humidity are close to none.
Did you have a problem with this lens? Will you elaborate?
5D Mk III, Elan 7e, Fuji X-E1, some old rangefinders
Tamron 24-70 2.8 VC, Canon 70-200 f/2.8L IS II, 400mm f/2.8L II, 100mm L IS Macro, Sigma 85mm, 50mm, & 35mm f/1.4's, Rokinon 14mm f/2.8, Canon 2x Extender II, Kenko 1.4x, 430 EX II, Elinchroms