I searched threads bit didn't quite find what I needed. Car is 86 cutlass two door. Interior is of no concern. Will only have buckets with no rear seat and will have a vfn 'glass dash. HVAC will be gone. Intend to tie in from in front of front wheels to rear of rear wheels. Prefer to weld directly to frame then weld body to cage. It wont have to be class legal just safe. What diameter, thickness, and material should I use? I saw some answers on material but they were abbreviations I didn't know