Atco grassbox weight

My B30 Atco (circa 1980's ) is fitted with a thick plastic (HDPE?) grass box that weighs 5.9kg (13 lbs) when empty. That's nearly a stone in old money without any grass! 

It makes emptying the grass  a real chore. Does anyone know if the current  Allett models still use these heavy plastic boxes or do they use a lighter material?  

I kept my grass box from my previous Atco Garden 30 which is made of aluminium and as light as feather but unfortunately the shape and the mounting arrangements are totally different.