Motorsport and frame welding

Ideally the car will be used for driving on the road, but a great passion of mine is to be able to go racing. The idea behind the WRX which went so horribly pear shaped, was to get it on the track and join in for some hillclimbing and supersprints. I've got queries about putting a rollcage on the car. It would be an intelligent move to incorperate a roll cage when i am building the frame, before the bodywork is put on.

So looking at putting a half cage in. According to the CAMS Manual of Motorsport, a half cage is the minimum required for open wheeler in "Speed" events like supersprints and hillclimbs. It will need to be made of chromoly, circular section dold drawn tube. The main hoop needs to be 44.45mm outside diameter and 2.5mm wall thickness. All other components will need to be 38mm outside diameter and 2.5mm wall thickness. The supporting pads of the cage will be welded to the main chassis and the rear support bars will be welded to an extra rear structure which will need to be designed into the chassis as it is being built. The pads themselves have a specification to comply with. Each mounting foot of the front, main and lateral roll bars must include a reinforcement plate, of a thickness of at least 3mm which must not be less than that of the tube onto which it is welded. Each mounting foot must be attached by at least three bolts on a steel reinforcement plate at least 3mm thick and of at least 12,000mm2 area which is welded to the bodyshell. Examples are shown in drawings 253-18 to 253-24. (For drawings 253-18 and 253-20, the reinforcement plate does not necessarily have to be welded to the bodyshell.)

Having a chat to a fella from work, i have been advised it would be advisable to tack weld the frame and cage using MIG but with 0.9 309 stainless steel wire. This will help with the final welding of the frame and the cage, as i would like to get the frame TIG welded by a ticketed structural welder.