Bonding sideskirts on?

If there is enough meat to get a few good rivets in the return edge at each end (the bit that laps into the wheelarch) then as long as the skirt isn't too flexible, some strong tape should hold it on OK as long as the surfaces are nice and smooth and clear or grease/dirst.

I've had sideskirts before that had no tape, adhesive or fixings along the top edge and just relied on the fixings in the return edge at either end (screws on mine) plus about four more along the underside of the skirt where you can't see them...going into the sill. No further fixing was needed and it was rock solid.

EDIT: After the major hassle Rich had removing some 'pods' from a BX the other week that were fixed on with a sikaflex/tiger seal type mastic, I really wouldn't go down that route unless you really hate your car and really hate yourself.

If they never ever need to come off again then Tiger seal, otherwise silicon sealant and rivets - i've actually come across kitchen wall units held in place solely by silicon - it does need a decent amount of space to spread out over though to get a decent strength of bond and a good drying time.

+1 for tiger seal. As sticky as it gets. Just don't get it on hands without removing immediately.