Way to lower vassal integration cost

Set their behaviour to passive.

You can change a fleets behaviour in the fleet window (bottom left), can't provide a screenshot right now, but should be easy to find.

There are three options:

• aggressive: fleet automatically attacks hostiles
• passive: fleet won't attack on its own, but will defend itself
• evasive: fleet retreats as soon as enemies appear.

non-combat ships are on evasive by default and as such they will run immediately, when a hostile is in the system. I recommend setting them to passive while exploring, but evasive, once you get in a war.

So to upgrade your fleet you first need to update the ship design, you can go into the ship designer in the top left and add the Coilguns. What I think you may have done wrong is created a new ship design and added the Coilguns there instead of updating your current Papillon-class Corvettes. When you change your ship design make sure you are modifying the Papillon-Class corvette and not creating a new class.

If you want to change the name of the class you can do that in the ship building screen, if you create a new class it won't change the existing class. Once you have update the Papillon-class and/or renamed it the upgrade fleet button should be Colored.