Furnace ducting issues

[Nomadicchefs]

We had the vents scoped by a supposed rv tech to check for any pinching, damage, etc of the duct work between an extremely warm vent and the next one in line. He stated there were none. However, it still bugs me that there is such heat fluctuations happening. So, I got one of those cheap snake cams from Walmart and I am in complete shock. Someone please tell me, how do I repair holes or gouges cut too large and tears from installation? Where the actual duct plenum fits into the main line ductwork, the hole was cut jagged, there is about an 8"x1" cut that is definitely allowing heat to escape, and although the pics are rough, you can see the gaps and jagged edging where the plenum fits in, the 2nd edge of it is bent/pinched and not very flush with the ducting at all. I know I can get to it via the underbelly, but is this something I can mend with the foil tape or should I seam in a whole new piece of duct into the main line where the plenum fits into it?

I understand how the heat is meant to radiate into the underbelly to give it the "arctic package" keystone proclaims, but the 8x1 gouge I'm talking about is directly below the kitchen sink area. Our furnace sits diagonally to our sink, but the heat radiated within the cabinet is more than enough to prevent water line issues, so the gouge isn't there on purpose. I snaked the entire camper, there are no side winding ends that jut off to allow heat to radiate out to holding tanks or the basement areas, but at the back of the kitchen and the bedroom areas where the ducting ends - there aren't end caps stopping it anywhere it's just crumpled up and stuffed up into itself, almost like waded up paper. If that's the norm, no problem then. But as for the other issue, I think I should definitely do something about it while it's still warm out.