I often hide underneath a crippled boat while reloading, or under one that's moving a la Down Periscope. Works great in the game but I doubt it could be done for a real tactic.
As others have done, I too have sat in the front of the convoy watching that lead destroy zig-zag his way towards me. In one instance, I had a type iv acoustic loaded aft and as soon as he'd gone past me, I started lining him up for a shot. I managed to sink 2 tankers, a liberty and cripple a C2 while the acoustic @^#% DESTROYED the DD (massive explosion! MASSIVE! Must have hit the ammo).
Diving down to evade the retaliation, it always seems like it takes forever to reload. Those DDs were pissed at me too because they kept tracking me for 2 hours while I kept popping decoys and moving away.
Don't forget to use your recognition manual! I've only learned of it's importance recently and getting critical hits to a boat can save your neck.