Setting net.ipv4.ip_forward=1 is troublesome for various reasons, including security.

Would it be possible to stop using that and instead use something like iptables rule below instead?

Example for container started with --port 0.0.0.0:29418:29418

iptables -I PREROUTING 1 -t nat -i eth0 -p tcp --dport 29418 -j REDIRECT --to-port 29418

This should work, though translating 0.0.0.0 to eth0 is a potential problem. I'm not an iptables wizard, so there is certainly a better way to do this.