Heatwave may work on bigguns, maybe, if you pump out enough flame it may build up to a stumble, perhaps...We'll see!
That's a good idea with the trenchgun, didn't even think of that! I've only been thinking about the flamethrower in relation to these, which was silly!
Honestly when I saw splash damage, I related it to the flamethrower, maybe the caulk 'n' burn and maybe the microwave gun, possibly trenchgun too. I would have thought it meant either the width of the cone or how large an area a flame impact effects. Splashing off a wall around a corner or hitting one zed and burning the ones adjacent to it, for example.
If it's the latter it'd affect the trench gun too I'd say, if it works like KF1 where each pellet had a small aoe impact.
I like the last skills too, I am leaning towards the flame explosion one aswell but I'd be rushing to get a kill every time, likely using up ammo! Though I like the sound of the second one if firing on bigguns is okay this time.
Microwaves cook from the inside out, no? I bet it'll be a hard hitter for tougher stuff, I hope so anyway!