3M's double sided fabrication tape should work - it's all they use to
hold the aluminium bodywork onto modern buses.

Otherwise the urethane sealant used for fitting windscreens gets a
bloody good grab if you clean the surfaces first (used by Ford for
factory fit body kits).

Lumiweld and similar aluminium soldering products work
pretty well in my experience, but although the melting
point is less than that of the panels it's not that much
less, so there's a significant risk of large areas of the panel
falling off if you're a bit cack handed with the heat.

For dealing with small holes I'd get the metal as clean as
possible front and back, then araldite aluminium foil to
the back before filling the front.

Nick