Having lived in Michigan for the majority of my life, I will add one more thing to the conversation. In my experience, trailer brakes that sit unused most of the time tend to rust up and not work. There are several parts in there that must move to actuate the brakes, and if they can't move, the brakes won't work.
On the flip side, if they do move, and there is rust, they can hang up and result in the brakes dragging.
I suggest pulling the hubs, and checking all the brake components. Clean up the pivots, and lightly grease them for best resistance to rusting up. Once everything moves freely, the brakes should work pretty well. FWIW, with the tiny brakes used on most small campers, you probably won't be able to lock them, even with the controller cranked.
I have a Prodigy P2, and would recommend the Prodigy series to anyone considering a controller. MUCH better performance than the time ramp units, which are just about useless in a panic stop when you need trailer brakes the most. Much smoother than the pendulum type controllers too. P3 will even tell you if there are problems with your brake circuit, or magnets. Can't beat that!!