[JRTJH]

There are at least two "screwed in place" panels in the basement. Look for them, remove the screws (probably 4 on each panel) and you can access most of the ductwork, wiring that's under the steps going up to the bedroom, plumbing for the gray and black tank, shower, bathroom sink and black tank flush and the back of the water heater. The ducting from the underside of the main cabin floor runs up through the floor into that area of the basement, connects to the duct that's against the ceiling of the basement storage and the underside of the aluminum ducting for the bath/bedroom is attached to the top of the basement storage.

I would leave the coroplast alone until you check the condition of the ducting behind the basement storage. That's much easier to access and often is the location of any kinks or twists in the round "dryer vent hose" ducting.