It helps keep the rain off, back in camp (3)
I believe the answer is:
mac
This clue might be a double definition.
'it helps keep the rain off back' is the first definition.
The definition suggests a singular noun which matches the answer.
'camp' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'in' is the link.
Can you help me to learn more?
(Other definitions for mac that I've seen before include "Raincoat (colloq.)" , "It may help you keep dry" , "A Gaelic son, often in name" , "Waterproof raincoat, in short" , "A rainproof" .)