RE: Wing Tube question
You should be able to order a new tube separately, don't use a wood dowel or the tube you cut. Sig list a 15-1/4 INCH ALUM WING JOINER TUBE for $10.25 it is part #SIGRPAT276, I'm not sure if this is the correct one for your Somethin' Extra or not, check your manual and see if they list the part number.
They also list a 15-1/4 INCH ALUM WING JOINER TUBE FOR SOMETHIN EXTRA ARF Part #SIGRPAWJ76ARF for $19, not sure if it fits the kit or not though maybe Somethin Extra owners can chime in and let you know for sure. Any Sig dealer should be able to order it for you or you can order it directly from Sig's Website