I am not up to date with joining metals with heat (except for a little silver soldering), but I was well up to speed on strengthening model boat hulls to take the stresses of sailing.
We used to use carbon fibre rod, available from good model shops or fishing tackle shops, and bond it with resin and glass tissue along the areas that require strengthening. I think you can even get tube nowadays in very small diameters.
In conjuction with a friend (sadly gone elsewhere), we used to produce for other club members, the lightest glass hulls you could imagine, mainly scale MTB hulls, just one layer of chopped mat thick plus gel coat in most places. Just a few inches of CF rod bonded down the sharp pointy bit at the front would almost make the hull strong enough to chop wood with. Do that in all your problem areas, and not only do you keep the weight down, you make an immensely strong and rigid hull. You can (or used to be able to) get the rod down to 1mm diameter, so you could bend and bond it along almost any internal chine line. Or you could bond it diagonally in a regular pattern to flat panels to make them super rigid.
Just maybe another cure for your problem.