Hey, I suggest you read
Just finished downloading the entire blockchain. How can I help the network now? thread. There is an explanation even if you didn't open up your 8333 port, you are still being a useful node.
I also listed a reference about how to open the portfoward the port there. If you still somehow couldn't port forwarding it, I suggest you run the node over Tor, since it will automatically opened up your ports, and you will get better privacy, as @jackg suggest.
Regarding VPN, AFAIK, Bitcoin node would not prioritize non-default ports--since if you use VPN, you will have a different port for the remote port forwarding, so, I don't know for sure it will be helpful or not, I personally, haven't tried it out myself.