If your brake pads are tight on the disc they would overheat and burn quickly. Generally, you will find some residue continually as you use the trailer- depending of the amount of heavy breaking you have to do. I have the tandem with a Z18. The brake axle wheels always accumulate some brake residue but not a lot. Take the wheels off and check you brake discs to be sure they seem smooth, and not warped any way.
I've learned it's a good idea to remove all the lug nuts at least one time each year to be sure they dont get stuck or seized. That's an opportunity to roll the wheel bearings by hand to see how they feel. Same thing with the Propeller nut.