Waterproof garment from a popular company carried by deserter (8)
I believe the answer is:
raincoat
'waterproof garment' is the definition.
(coat worn when it's raining)
'a popular company carried by deserter' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'company' becomes 'co' (abbreviation).
'carried by' indicates putting letters inside.
'deserter' becomes 'rat' (both can mean a traitor).
'a'+'in'+'co'='ainco'
'ainco' going inside 'rat' is 'RAINCOAT'.
'from' acts as a link.
(Other definitions for raincoat that I've seen before include "Macintosh - with 22a" , "protection against the elements" , "Mac" , "Protective garment for Croatian" , "Outer garment for Croatian" .)