What I did was put the following into console and I was able to host a server with friends:
maxplayers 32
map mvm_mannworks (decoy or coaltown works too!)
sv_lan 0
map mvm_mannworks (or to decoy or coaltown. have to change maps for this to kick in. Didn't check if you could do it before launching map.)
Then you just give people your IP,
the IP that is listed here.