Google cloud's ssh command lets you pass standard ssh flags. To, for example, forward local port 8088 to port 8088 on a vm instance, all you need to do is:

gcloud compute  ssh --ssh-flag="-L 8088:localhost:8088"  --zone "us-central1-b" "example_instance_name"

Now browsing to localhost:8088 works as it would with standard ssh.

start new:

tmux

start new with session name:

tmux new -s myname