: In my next life I will use box section
: aluminium as a strongback.

I am using a Ted Moores type boxbeam for my first kayak, and it is solid as a rock. If I decide to build a design calling for an internal strongback (and I might) I've thought about rectangular aluminum tube. But I wonder if anyone has tried the glued-strand engineered woods? These are much stiffer and more warp-resistant than regular wood, and still take screws (unlike aluminum). I don't know what this stuff costs, but aluminum's not exactly cheap, so maybe it'd be a good alternative.

Glad to hear all your problems worked out in the end.