So these 77L trays look interesting, 2 in deep and average size
http://www.containerwise.co.uk/propagation-trays-350-215.html
and David at Containerwise has offered them at £3.90 each inc VAT plus delivery, minimum order is 16 trays so I am doing that and it should be worth it for the time they last (15 years). Email them via their contacts if interested, mention David’s name and this offer.