Covered outhouse, full of warmth (8)
I believe the answer is:
sheathed
'covered' is the definition.
(sheathing is a kind of covering)
'outhouse full of warmth' is the wordplay.
'outhouse' becomes 'shed' (I've seen this before).
'full of' means one lot of letters goes inside another.
'warmth' becomes 'heat' ('heat' can be a synonym of 'warmth').
'shed' going around 'heat' is 'SHEATHED'.
(Other definitions for sheathed that I've seen before include "put in protective cover" , "Of sword, placed in scabbard" , "Covered for protection" , "Encased in close-fitting covering - say sword" , "Put sword back in covering" .)