4' wide trailer ???
Checkout the kitab containers at Bunnings.
Been using them ever since BigW first started selling them years ago.
3 x size capacities ... but are all the same length and width ... just different heights ... length is 600mm ... so - two end for end, fill the trailer width and prevent moving around.
Check the actual trailer internal measurement tho ... 4' isnt always 4' depending on who did the welding.
Crappy lids are available and need some sealing tape. i made up one timber lid that covered three (or whatever) rows of tubs that held them all in place,
Different colours for easy ID of contents
Heaps stronger (and more expensive) than the weak clear plastic ones. Save some space by using them as washing up / bathing buckets as well.
The milk crate sized Nally Cube style that Bunnings also has access to ... have the same base measurement as 2 x jerrycans ... and can be handy as well.