Morning Steve,
I would suggest removing the rear lights on a 9-3, though I am not that familiar with their construction.
On the 9-5, I removed the wheel arch liners, which gives great access - it is very straightforward to do,
The spray system was used for all those difficult areas you cannot reach. Mix 2 parts waxoyl to 1 part white spirit, then stand the container in some very hot water for 10 minutes before use.Ensure you get the maximum pressure in the container to ensure a fine wide spray pattern. If you do decide to follow this method make sure you have some old cloths and plastic containers to collect the excess waxoyl - it can get rather messy!
Finally be warned, it will smell in the cabin for a few days until the wax hardens, so try and keep the windows open when possible.

PS: I used Flag rust remover and paint (made for the marine industry) for the inner arches, I also used rust remover followed with Tetroseal sprayed on to the chassis.
