Linkabord Raised Beds 600 mm high: advice on structural support please

Hello from a new member in Ely, Cambs. After several years of bending & crouching over my 5m x 2m plot at home I'm going RB & want to use recycled plastic material. I've found Linkabord among the best (not cheap by any means, but not ridiculous compared to others, and there's a 10% off code from this site ... ) BUT they advise no more than 3 kits high ie 45 cm. I'd really like 60 cm high.
I quote from an email response: "We recommend the maximum height of 45cm purely for structural strength - anything over this may not withstand the weight of the soil for a long period of time."
So my question is - what might I do to reinforce it? I cannot drive nails thru as that will destroy the double-skin. What about using plastic posts on either side of the bed wall with a cross bar anchoring them, doing this every 1 m? Or re-bars? Any more aesthetic solutions? Has anyone had experience of 60 cm high Linkabord beds & if so how has it stood the test of time? The bed will be 3m x 1m. I may be able to fit in a smaller one too. All responses gratefully received!

Hello from a new member in Ely, Cambs. After several years of bending & crouching over my 5m x 2m plot at home I'm going RB & want to use recycled plastic material. I've found Linkabord among the best (not cheap by any means, but not ridiculous compared to others, and there's a 10% off code from this site ... ) BUT they advise no more than 3 kits high ie 45 cm. I'd really like 60 cm high.
I quote from an email response: "We recommend the maximum height of 45cm purely for structural strength - anything over this may not withstand the weight of the soil for a long period of time."
So my question is - what might I do to reinforce it? I cannot drive nails thru as that will destroy the double-skin. What about using plastic posts on either side of the bed wall with a cross bar anchoring them, doing this every 1 m? Or re-bars? Any more aesthetic solutions? Has anyone had experience of 60 cm high Linkabord beds & if so how has it stood the test of time? The bed will be 3m x 1m. I may be able to fit in a smaller one too. All responses gratefully received!

I would disagree the price is excellent 1 metre x 3 metres x .6metres is £189.50.   Wood won't last. Have you thought of raising it up. Breeze blocks, bricks or concrete wall as in footings but don't stop at ground level. PS coupon please.
 PS it says 60cm on the site.
https://www.linkabord.co.uk/product/60cm-high-raised-bed-kit-available-in-all-6-colours-and-all-sizes/

I must be getting old, I think that's a horrific cost for a couple of lengths of plastic,have you thought about something like gabbion cubes. Either for the project entirely or for a foundation to raise the linkboard beds ups.