My cartons start out as hand drawn but most of my work is done in Corel Draw for the clean lines and then eprted to Photoshop for the colours.
I do have some though that the lines are all done by hand with ink and a brush, then they are scanned and coloured in photoshop. It all depends on the effect I want.
The attached Ballarat Rod Run design was done with the ink and brush method for the cars and starter then the rest was done with Corel and then finish coloured and separated for screen printing in Photoshop. The others are also the same style of artwwork.
I believe this was how a lot of the later Ed Roth work was done using ink and brush for the lines and the photoshopping the colour.