Reply to "How are the wheel skirts included with Aero train sets attached to the side wheel frames of the locomotive's front trucks?"

They screw onto the top of the existing sideframes.  There are four flat head screws that should come with them to attach them (two for each side).  I put a set on one of mine, but it hits the shell, so they'll have to be "adjusted" before they can be used.

You don't have to take the trucks off, just swivel them out and plop the skirts on and screw them down.