Store with mass of stuff in Teesside location (8)
I believe the answer is:
stockton
'teesside location' is the definition.
'store with mass of stuff' is the wordplay.
'store' becomes 'stock' ('stock' can be a synonym of 'store').
'with' says to put letters next to each other.
'mass of stuff' becomes 'ton'.
'stock'+'ton'='STOCKTON'
'in' acts as a link.
(Other definitions for stockton that I've seen before include "From here, early passengers" , "Town near 1 Across [REDCAR]" , "English town with former castle" , "- - -on-Tees" .)