What running gear do you have? aka what axles, t-case, etc. including make and year.
I have an E-brake from http://www.highangledriveline.com/E-...plications.htm
that goes on the output shaft of my 205 t-case. It works well enough to stop the truck on anything the tires will grip on. Some vehicles (like motorhomes) had driveshaft mounted e-brakes...most of them were drum.
The problem with wheel disc e-brakes is that they weren't meant to handle the added leverage of large tires and low gearing. Drum e-brakes work good at the wheel but only forward.
I think your best bet is a driveshaft mounted disc or drum.