Here's an idea I read a while ago. 
  
I think it was in sportcompactcar "before it became a crappy primedia sh*t rag"  
  
They used expanding foam sealer in the rocker panels to stiffen the chassis. 
  
I know I can get this stuff in different densities at hardware stores. 
  
The question is, could I use this to inject into the hollow members of the shell like, rockers, A,B-pillars and the rim of the roof to stiffen the chassis (for street use) around the passenger compartement instead of having tubes around. I'd still use a dash bar, main hoop, fr. & re. strut connectors but, no links between main hoop and the front part. 
  
Thanks. 
  
P.S.: I know many people have told me that "You know what happen if water gets there. Keep moisture... but, does'nt the foam forms a slick seald layer on it's surface when it's dry? Plus the car would sit in a garage and rarely see the rain.