Handheld router with a bearing guided cutter and use the router fence. What you will need to thick about is how to hold the skirting for cutting. You do not want to try to balance it on something as you need to concentrate on the router and stopping it tipping.
Assuming you are going to screw or nail it to the wall use the holes to screw it to something to hold it still.
Mick
Assuming you are going to screw or nail it to the wall use the holes to screw it to something to hold it still.
Mick