Rusty underside box section frame !
Does anyone have any ideas about replacing sections of the box frame on the underside around the edge on my Eriba Familia 320 gt. it is from the back of the wheel to where it bends up just before it goes round the back . I’m presuming I can just cut out and replace the length and weld back in , but I am wondering how i isolate from aluminium edge and plywood floor while welding. It’s probably obvious and the aluminium needs removing and floor taken out but seems a bit drastic. If someone has atempted it before without doing this , I thought I would ask .

Cong-le-Ton, not far from Macc-les-field