I have the luxury of a "cutting laser" to cut routing templates, however, they could probably made with a scrollsaw/jigsaw (carefully).
My
Hummer build should detail how I do it... though
Master Yoda Dutchy could provide better insight... though he now has a laser as well (sorry for the reveal Dutchman).
If your first cut is too short... Take the second cut from the longer end... LBD