Base occupied by son as resting place (5)
I believe the answer is:
roost
'resting place' is the definition.
(I've seen this in another clue)
'base occupied by son' is the wordplay.
'base' becomes 'root' (synonyms).
'occupied by' indicates putting letters inside (inserted letters occupy or enter the word).
'son' becomes 's' (genealogical abbreviation for son).
'root' going around 's' is 'ROOST'.
'as' is the link.
(Other definitions for roost that I've seen before include "bed" , "Settle down (on a branch?)" , "Temporary place to stay" , "Rest on a perch" , "Bats' settling place" .)