That's the standard ply lining install method unfortunately...
It's the same on all vans...
Infact on my sport line, they used screws that were so long that when I fitted the towbar, I couldn't remove the spare wheel.liner as they had screwed right though it, in multiple places...they was about 5mm from Going into the tyre.
If you get under the van and remove the plastic under trays you will see the holes made by any previous ply lining.... Especially on ex panel vans aka as above - builders vans.
And that was ply lining fitted by the main dealers contractor on a brand new van.
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The only silver lining is that it comes out easy when you remove it.
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But agreed it not ideal, and I wouldn't do it on my conversation.... Glue,buttons,boards, sand bags weight is how I would do it.