Your NAT rule is wrong…
Try:
chain=srcnat action=masquerade src-address=10.17.14.16/30 out-interface=WAN
If your intention was to masquerade traffic to your tunnel, use
chain=srcnat action=masquerade out-interface=tunnel0
No need to specify an address on masquerade, since masquerade means “src-nat to the interface address”.
Also check that forwarding is allowed both ways between WAN and tunnel0.
This route is useless and wrong (but without any side effect) because of the /32 mask. Usually there are no packets with destination address 0.0.0.0 on a network:
1 A S 0.0.0.0/32 10.17.14.18 tunnel0 1
To use a default route to 10.17.14.18 and then redirect the reply traffic from there back to WAN, you need to use dst-nat, routing marks or VRF since there is only a single default route for a given routing table active at a time.