"Chris Reed" wrote

I've had the brakes checked out by a garage (auto repair shop in US?) and
all is fine, but this still happens. My guess is that somewhere in the
brake mechanism is a narrow clearance which tends to lock up with
corrosion.

Most all drum brakes on automobiles have strong springs that forcibly pull
the brake shoes away from the drums, nearly all of the way. Only a small
part of the pad would be touching the drum in one small area of each shoe.
That is when the adjusters are working well and are keeping the pads out as
far as they are able. Most are not working well, and have a good bit of
slack that the brake piston has to take up when you press on the brakes. A
shoe in this condition does not have enough contact area with the shoe and
drum to rust together.

I am not familiar with this particular model of brake, but with most cable
actuated brakes, there can not be a lot of clearance from the drum, or the
cable movement would be too small to take up the slack and apply the
stopping pressure. It is the nature of the beast that the design must have
the shoes in closer contact to the drum, thus increasing the likelihood of
the two parts rusting together.

It might be a good idea to back off the adjusting nut, or star wheel
(whatever your model would have as an adjuster) before parking the trailer
for the winter.
--
Jim in NC