Howe's strike completed a remarkable comeback for the Gulls, who had been 3-0 down at rain-lashed Plainmoor in Tuesday night's League Two clash.
Howe's seventh goal of the season capped a memorable night for Martin Ling's side as substitute Ashley Yeoman levelled in the 84th minute from Lee Mansell's cross.
Fellow sub Ryan Jarvis slid in to make it 3-2 in the 69th minute after unselfish play by Howe.
Billy Bodin sparked United's incredible revival with his 48th-minute close-range strike after a superb double save from Shots keeper Jamie Young to deny Nathan Craig and then Howe.
Shots striker Craig Reid completed his quick-fire hat-trick in the 47th minute after Danny Hylton's strike was saved by United keeper Michael Poke.
Reid opened the scoring on 28 minutes when he steered in Alex Rodman's free-kick from the left, and then doubled his tally from a 37th-minute penalty after United right-back Joe Oastler fouled Hylton.