I think perhaps I need to think about going up rather than forward.
Perhaps by putting some sort of rack on the fridge box and putting the
Aquarolls up there. Or maybe by finding a way to attach a set of roof
bars to the trailer so I can strap the Aquarolls up there.

I'm not sure 90kg up 2m high above the axle is much better...

From a physics point of view, an underslung attachment just fore and aft of
the axle would be best, if this can be accommodated by the trailer structure
without road safety issues.

Christian.