I Was wondering if anyone can give any tips for constructing a new transmission tunnel in a race car.

The car is FWD so the tunnel is only for the exhaust pipe. We need to remove the existing tunnel which is too small for the exhaust/oil lines etc which will run down the centre.

We will replace it with one which is larger, and I was wondering if anyone could give some tips on tig welding the new tunnel to the existing floorpan. would one tig weld along the full length of the tunnel (from the firewall to where the floor pan kicks up for the rear seats etc) or would you stitch weld it?