Sorry to hear that Jan! You could maybe cut down a small syringe tip for the cannon barrels? Or carefully remove the wires from a thin diameter (but fairly rigid) electical wire, and use the hollowed insulation for them.
As for the wing-root gap, I use either liquid cement, white woodworking glue (PVA - Polyvinyl acrylate), stretched sprue melted in liquid cement, or thin plastic sheet wedges to fill them, depending on size of gap. I only use putty if I have to (like now with the Me 163 panel lines), in which a thin wash of nail polish remover helps confine it to the required area, or atleast a waxing with Tamiya compound when it's dried will clean it up nicely too.