what did you use for the false floor mate 18mm ply?
The false floor was made with 4x2 for the long supports from the wheel arches forward and just behind the wheel arches to the back
Then for the cross supports I used some old steel box section (old council green posts) on top of the timber.
To brace the space where the wheel arches are I used cls (happened to be same size as the steel)
So because it's all braced and supported well I only used 12mm ply for the floor itself.
It's going nowhere.
It needs bracing because even with 18mm the span is too great it would sag under constant load from gear and tools.
The way the back is you need the full width more or less between the arches to get a full proper 8x4 sheet in so I had to get a bit creative with the bracing there.
The original plan was to run 4x2 all the way front to back just inside the arches and cross brace with box section but became aparrant that you couldn't do it like that as you need the width arch to arch.
Originally my mate was just going to knock me up a full frame from box which would negate any need for clever bracing but he was real busy and I needed it doing asap so set about it myself.
All your basically doing is running front to back with timber and cross bracing all the way along bracing the width by using steel it stops the sagging issue and the bracing between the arches with timer give added support to that area as that's where I put all my bags of gear
There's enough room to get 6 8x4 sheets of plasterboard in.
I work alone generally so that's plenty for me any more and I get a delivery.
It takes the hassle away from only needing a couple of boards and having to wait on delivery which you can look a little amateurish booking a delivery for 1-2 boards