Very much involved, want to enter tower (4-4)
I believe the answer is:
knee-deep
'very much involved' is the definition.
(I've seen this before)
'want to enter tower' is the wordplay.
'want' becomes 'need' (synonyms).
'to enter' indicates putting letters inside.
'tower' becomes 'keep' (I've seen this before).
'need' placed inside 'keep' is 'KNEE-DEEP'.
(Other definitions for knee-deep that I've seen before include "Immersed up to the patella" , "Thoroughly involved (in)" , "Deeply involved (in something)" , "(Of water) over the top of one's wellies?" , "Submerged to one's patella" .)