This is difficult to answer because the application issues are numerous. Wire coating faces problems with Faraday areas as well as aerodynamic issues that can occur as the powder and air travel around the wire and intersections. Unfortunately, E-coat, although providing additional protection in difficult areas, adds to the application problem. Having the parts E-coated at a different location and then rehung on your line increases the resistance, making electrostatic dissipation more difficult. The E-coat can be charged by the ions generated with corona charging equipment and, as a result, make penetration and coverage even more difficult at the welds and wire intersections. The advantage of the tribo guns is the minimal amount of external charging field that the guns generate. The disadvantage is the relatively poor transfer efficiency and high labor required. The effects will be the same with a corona gun that has to be "tuned" back so far to reduce the charging issues enough to allow coating those tough areas.
Is tribo the only way or best application? It may be. However, the only way to determine which is the best is through testing with more than one formulation with a number of conditions, such as potentially preheating the parts to enhance performance in those weld areas. Automatics will allow you to apply more consistently, although it is probably not realistic that automation by itself will eliminate the need for manual reinforcement. Another alternative is to explore other methods of rust prevention, such as conductive primers. Take a close look at the fabrication and design of the products as well. Maintaining good spacing practices for the wire (minimum 1.5 times the wire diameter), high quality welds to eliminate trap areas and clean cut off of the wire, bar or other materials that will reduce sharp areas, the first to fail, will enhance the application.