Help needed Kamailio NAT Issues (not commercial) - open to bidding

I am in the process to configure Kamailio with Asterisk for personal use. Below are the setup details: - Asterisk and Kamailio on one VPS with 1 public IP - Asterisk listening at Port XXXX - Kamailio is listening at port YYYY - No P2P calling Kamailio is acting as registrar and Location server at the moment. INVITES are being forwarded to asterisk by Kamailio. I AM FACING THE NAT ISSUES BECAUSE THE EXTENSIONS ARE BEHIND NAT. ONE WAY AUDIO OR NO AUDIO AT ALL WHEN CALLING. Tried rtpproxy but it seems I am not the expert of configuring routes in Kamailio so I am looking for someone who can help me to fix and understand the issues. Budget: Setup is for my personal use so I don't have any budget in my mind but if you can tell me how much it would cost then we can easily proceed.