You don't really make a masterboard with the Mayhem sets. The term masterboard I believe means having a set arrangement of tiles glued down to a single board. Kanelinx is an unofficial mod of sorts. It uses the Paperlinx idea and modifies it a bit by not having the actual link be exposed on the surface, creating a more seamless connection. I think for your needs you might want to use the Chunky Dungeons method. It's a little bit expensive though as it uses lots of velcro. The article shows you how to do it.

Edit: After reading the Chunky Dungeons BIAT it uses the term "pro-materboard." So maybe just a set maximum size?

Have you seen the post? This modual contains a new way to base up GR- which does away with the large board idea and brings it more into stream with SoM.

Lord Abaddon of Wormwood