Hello,
i didn't tried to build an vpn through the device, my vpn's are ending at the device. Try to check the logs of the ASA, to see if anything is dropped by acls.
Ping is a bit special. I had to allow the following icmp-types on input access-list on the external Interface:
Echo-reply (this is needed for Ping-Replys)
also you should allow the following types:
redirect
time-exceeded
traceroute
unreachable