Somewhere there is an option to show join messages in the text window not a dirty great pop up screen.
People can join a GV, It's handy to have.
If you want to get in and clear an area in a T34, grab a squaddie, the worst shot drives, the better shot joins and jumps in the turret. The higher speed of the T34 makes it a harder target and with a full time driver it will easily outmanoeuvre other single player GV's.