Wow, scary. (Putting it mildly!)
Read up on loading your trailer: too much weight in the back (same as too little on the front) will exacerbate the sway tendency. There are several threads here that discuss this subject... I will help you search for them - sometimes the topic morphs.
FWIW, we are using a WDH on our Escape
21, pulled by a 2013 Ford F-150 pickup; my husband likes it very much. He feels our tongue weight is a little heavy for the truck; it would probably be okay without it, but it's better with. My only problem with it is the "drawbar" is huge and heavy. No way could I manage it myself (unless I rig something for it to rest on while I shove it into place; a bridge to be crossed at some point). The ride is very smooth. (The Escape
21 is tandem axle
, which I think is the same as your Bigfoot.)
Sorry I don't have much concrete advice... But I'm definitely sympathetic to your situation. Again, learn about tongue weights (10-15% of trailer weight) and how to load things... Where are your holding tanks, relative to your batteries and refrigerator
, toilet, etc.? It could be the trailer is designed to have some water in the tank to offset the weights of the heavy appliances - although I am speculating. Hopefully, someone who knows more about your trailer will chime in here soon.