I like to keep my unit with the hoses attached and essentially ready to go.
To do this you need a box 80x55x40cms.
Solent Plastics do a large crate with lid. Model No: 21C62 and they cost £40.
See here - Last item at bottom of the page.
Solent Plastics for Plastic Storage Boxes, Plastic Crates, Plastic Containers, Big Boxes and Trunks, Home and Garden Storage