Actually I'm not convinced that aluminium is more damage-resistant that fibe-glass.
Just today I talked to a guy who had built campers using both. And he said that alumunium was morew fragile and almost unrepairable at the same time. If you get a dent there's just one option, replace the panel.
Fibre-glass does'nt get dents and if you damage it you can easily repair it, just sand, fibre-glass, sand and the paint again.
This was his opinion...
Look at Nida-core, just do a seach here, that's what we plan on using.