I had the same problem with cornering. Going up Emory Pass on HWY 152 to Silver City, NM. At every turn the brakes would come on, until it went into trouble mode and was disabled. The only problem with that was with no ABS, I almost rear ended a shuttle van at Sky Harbor Airport a few days later.
I have most of the handling and electronic stability issues resolved and I'm still not sure if think this project was worth all the headaches.
A factory Sprinter 4x4 is definitely the easiest route. If you go with an up-fitter, make sure they are a reputable company that will provide you with excellent customer support, otherwise your dream could turn into a nightmare.
Attached photos are of the Westy on Tin Cup Pass here in Colorado. We finally get to have some fun with it.