Can you run a VPN behind a double NAT?

I heard a double NAT can introduce problems with VPNs, but I don't understand why. I want to have a LAN behind a double NAT that can be connected to using a VPN. My desired network would look something like this: internet --- ISP router/gateway with NAT --- LAN1 --- custom router/VPN server with NAT --- LAN2 I was planning on running the VPN on the custom router (which is running openwrt) and then exposing it by using port forwarding on the ISP router. Are there any issues with this setup?

Question by jnasworld223 on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.