I was trying to configure gpg to work under alpine this is what I have so far:

1. Install and configure gpg
2. Install and configure alpine

first link some stuff

ln -s /usr/bin/gpg /usr/bin/encrypt
ln -s /usr/bin/gpg /usr/bin/sign


then edit .pinerc
Display-Filters=_LEADING("-----BEGIN PGP SIGNED MESSAGE")_ /usr/bin/gpg --decrypt
_LEADING("-----BEGIN PGP MESSAGE")_ /usr/bin/gpg --decrypt

Sending-Filters=/usr/bin/encrypt --encrypt -r _RECIPIENTS_ -a
/usr/bin/sign --clearsign

Now when you send an email should ask for a filter use control-n control-p to select encrypt or sign ..

As nobody has sent gpg encode mail to me havent got a clue if the decrypt works but it should do ;)