Forget the complicated stuff like compass or latitude scale. the simplest tool to determine the right angle is a simple block of wood or plastic. Place a shadow pin in it by drilling a hole that is a tight fit for a short lenght of arc welding rod or even a piece of straight coat hanger. Drill the hole with a drill press so the shadow pin is exactly perpendicular to block surface. Place block on solar panel and adjust panel angle and direction so there is no shadow of the pin showing. the pin is now pointing directly at sun. As soon as the panel is angled off a shadow appears. You can either manually adjust the panel every 15 minutes or pick an average at local high noon then lock in the panel for the season. It has been mentioned that summer and winter angles will vary. This shadow pin tool also helps here. I tested it out while measuring the solar panel output. adjusting every 15 minutes makea big difference.
For permanent attachment place the block and pin along the frame do not let block obscure panel because it reduces output voltage.