Gidday
The rocker (or loadshare) is a pivot between front and rear axles that pushes one up when the other other goes down. Where as in a slipper set up if one goes up the entire trailer lifts resulting in a lift in the other wheel. This results in uneven load share.
With all trailer you want them nose heavy, the ball weight as it called should be about 10% of the all up weight.
The issue with heavy loads in single axle applications, other then tyre ratings, is the tendency for the trailer to pitch and unsettle the entire car / trailer combination.
Personally I would think twice before towing much over 1,000kgs on a single axle setup.
The challenge is that dual axle trailers are heavier and as such require a bigger vehicle to tow than a single axle, but that is the price of towing larger things.
Cheers
PB