Crawling entirely inside torn sunroof (2,3,5)
I believe the answer is:
on all fours
'crawling' is the definition.
(I've seen this in another clue)
'entirely inside torn sunroof' is the wordplay.
'entirely' becomes 'all' (all can mean entirely or completely).
'inside' indicates putting letters inside.
'torn' is an anagram indicator.
'sunroof' anagrammed gives 'onfours'.
'all' placed inside 'onfours' is 'ON ALL FOURS'.
(Other definitions for on all fours that I've seen before include "Maybe crawling" , "in a defensive position" , "using arms and legs" .)