I'm stumped with bottom clues. I may have gone wrong with something though.
12d Back door (7) p-s---n 1st letter may be K
18d Barely sufficient (5) s----
19d Discover (3,2) h-- -n (hit on)?
20a Munitions (8) -r------
22a Hollow (4) -e-- (deep, dell, dent,well )?