Flat-bottomed boat made by firm in the Devon area (4)
I believe the answer is:
scow
'flat-bottomed boat' is the definition.
(I've seen this before)
'firm in the devon area' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'in the' indicates putting letters inside.
'devon area' becomes 'sw' (south west of England).
'co' going into 'sw' is 'SCOW'.
'made by' is the link.
(Other definitions for scow that I've seen before include "ighter" , "Unpowered freight barge" , "Wide-beamed dinghy" , "Vessel" , "Low boat" .)