how to construct a harness bar without a cage?

[Mtrhd329]

I have recently started autocross in my truck and would like to stay in the drivers seat during these activities. I was thinking that some 4 point harnesses would be helpfull but there is not a safe way to mount them. I was thinking maybe a pipe wedged in between the outer cab walls from side to side behind the seats and welded to the inner cab wall as it passes through would be strong enough. Anyone have any ideas?