Serf on Kubernetes with external connectivity

I have a question specific to Serf (and not Consul as a whole).
I have a cluster of Serf agents running in a Kubernetes cluster. I want to add one or more agents outside the cluster.
Is there a standard or recommended way of doing this? I can expose each serf agent in my k8s cluster through say nodePort and that works fine but that does not seem like a reasonable/scalable approach.

I know consul can go across a k8s cluster but want to have a similar solution for my Serf cluster.