I use a P2P Shared Key tunnel… Not sure if this will help you but here is an example of my DD-WRT config.. And nothing is NAT from what I can tell. Straight routing.. pfsense site is 192.168.0.x, the other site is 192.168.50.x... 172.16.50.x is the tunnel.
Startup commands
# Config for Site-to-Site SiteA-SiteB
echo "
remote pfsense IP/Host
proto udp
port 1195
dev tun0
persist-tun
persist-key
resolv-retry infinite
secret /tmp/static.key
nobind
mute-replay-warnings
verb 3
comp-lzo
keepalive 15 60
daemon
" > SiteA-SiteB.conf
# Config for Static Key
echo "
-----BEGIN OpenVPN Static key V1-----
-----END OpenVPN Static key V1-----
" > static.key
# Create interfaces
/tmp/myvpn --mktun --dev tun0
ifconfig tun0 172.16.50.2 netmask 255.255.255.0 promisc up
# Create routes
route add -net 192.168.0.0 netmask 255.255.255.0 gw 172.16.50.1
route add -net 192.168.1.0 netmask 255.255.255.0 gw 172.16.50.1
route add -net 192.168.60.0 netmask 255.255.255.0 gw 172.16.50.1
route add -net 192.168.100.0 netmask 255.255.255.0 gw 172.16.50.1
route add -net 192.168.200.0 netmask 255.255.255.0 gw 172.16.50.1
# Initiate the tunnel
sleep 5
/tmp/myvpn --config SiteA-SiteB.conf
firewall commands, I need to tweaks these but they work… just can't ping the dd-wrt router but i can telnet/web into it
# private subnets (anything FROM these subnets)
iptables -A ALL_ACCEPT -s 192.168.0.0/16 -j ACCEPT
iptables -A ALL_ACCEPT -s 172.16.50.0/24 -j ACCEPT
iptables -A ALL_ACCEPT -s 172.16.60.0/24 -j ACCEPT
# Open firewall holes
iptables -I INPUT 2 -p udp --dport 1195 -j ACCEPT
iptables -I FORWARD -i br0 -o tun0 -j ACCEPT
iptables -I FORWARD -i tun0 -o br0 -j ACCEPT