Angles are personal preference the two outside ones of ours are angled to the side and to the front slightly....about 20-25 degrees and the middle two are only 10 degrees or so if I remember okky dokkky.
The main thing is angle them so you can get an even spread in conjunction with the rod holders on the gunnels and the bait-board for when your trolling.
But don't forget to make the top lip curled outwards a tad or have some plastic inserts to stop chaffing of the rods in the holders.
Also make sure they bung a little bit of flat (key) in the bottom for the gimbals to lock into.