Hi 1CoolZ71,
Welcome to the Heartland Owners Forum.
You must remove the mounting screws to take down the coroplast in order to access the underbelly. An impact wrench will make the job easier and is less likely to shear off the heads of the screws.
Sometimes you can take out a few screws on one side and peek inside to try and figure out what's going on.
As you said it looked like RV antifreeze, before opening the underbelly, I'd suggest inspecting the water line connections and p-traps inside the coach first. If your refrigerator has an ice maker and antifreeze was pushed into the refrigerator, don't overlook the water feed line to the refrigerator.