Krullibulls Ae86 BEAMS is the only way

[Bean]

I'm currently (on holiday right now) also trying my best on stich welding the chassis. The metal is very very thin, i.e. 1/16 (1.5mm) wire/rod is too thick and needs too much heat. I managed to get better results (that's for TIG, still need to test with mig for some areas) with a 1/32 electrode and 0.7mm wire, using the pedal and max of 35Amps
Hope this helps. Also thoroughly clean the surface, also the underside if possible