this probably isn't the most efficient method but it works for me:
download
portmap and open it to check if router is compatible, if not go to your router settings and enable UPnP or NAT-PMP
open blockland and press ~ to open console and find a line that says "UDP initialized on port #####". go to custom game, advanced, and set the port to the same one that was in the console.
open portmap and create a local port that's the same as the one in the blockland console, and enable UDP.
the server should be ready to run at this point