It all slots together

There are two pairs of cleats on the frames, and matching cleats on the bottom of the floorboards, so when you drop the floorboards down they have to locate properly and it all ends up like this


If you look at the cross piece on the underside of the floorboards in the top picture, you see it extends beyond the slats, this runs under the centre floorboard which is fixed in place, and helps hold things together.

The boards on each side can then be lifted out by raising the outboard side.

Easier, simpler, and cheaper than stainless steel hinges.

I think a bit of cord and some simple wooden Jam Cleats on the frames should hold them in place. The cord can simply be doubled through a pair of holes in the locating cleats on the bottom of the floorboards. Unobtrusive, cheap, simple.

I really should give things a wipe over before taking photos....

And somewhere to stand

The floorboards are made up of the centre which will be fixed, and the two sides, which which are removeable.
The battens which join the four slats on each side extend under the centre peice to fix them down.
A small batten at each end locates the side forward and aft. And some angled blocks (yet to be added) will locate the floorboards to prevent them sliding side to side.
They are sanded screwed together above, I have to take them apart and add a drop of glue, and then oil them when they are dry.

I'll have either turn buttons, or simple cords to hold the floorboards down on the outsides.