Hi Adrian,
What do you use to identify your ASA with the dynamic IP to the remote ASA with static IP? Take a look at this example:
I use this on my dynamic peer:
crypto isakmp identity key-id ASA1_ASA2
Which matches the tunnel-group on the static IP peer:
tunnel-group ASA1_ASA2 type ipsec-l2l
tunnel-group ASA1_ASA2 ipsec-attributes
ikev1 pre-shared-key ASA1_ASA2_KEY
Hope this helps!
Rene