Word to the wise
If you intend to keep the slipper spring, glue a plastic (oil impregnated if you can find some) pad on the chassis rail where the slipper moves.
Failing that weld a wear plate of at least 6mm thick where the spring moves. A few hundred k's on corrugations and the slipper will wear through the chassis rail....
Don't be tempted to fit shockies with that light load as it will make the suspension way too stiff and throw the thing all over the road.
I hunted down some old Valiant Regal springs for my trailer. Long and supple...
Looks good behind the wagon!!!