I'm installing a lot of stereo equipment into my car. As well as making some custom enclosures for the speakers out of GRP, I also need to stiffen the roof.

My idea is to get some 10mm thick 3/4" Aluminium honeycomb and some polyurethane 2 part expanding foam to make some panels to bond to the roof.

Would this be a suitable way to add significant strength/stiffness to a metal panel. here's a pic of my car roof

Each of those section is 900mm x 300mm. Any advice or other ideas welcome.

Cheers

Yeh PU foam isn't the most user friendly. But I think it could be done, in lots of batches. Just mix up 200ml or so, then pour it into the cells until you run out. Repeat until all the cells are filled. Wouldn't be tooooo difficult, would take a bit of time and a lot of cups trimming it neatly could be trickier than you think too.