TassieTiger wrote:You must be doing it up pretty right to get the steel flexing?
Could you put some spikes on to the clamps as to allow more bite into your timber “keel” for less pressure?
Not at all. In fact it flexes before it is tight enough to be secure. It is the sliding mount, with its single mounting bolt, that allows the movement. I have adjusted it to remove play, while still allowing it to move, but as soon as any load is put on it, the assembly tilts. In your photos I see that your stand is different to the Bunning unit. Perhaps yours is better designed.
Your idea is not bad, and I tried something similar on that clamping edge to stop the pivoting. I reduced clamping pressure enough to be able to lift the top out of the clamps with one finger, but it still tilted. I think any solution will need to be on the other side of the clamp, where the gap is opening up. A locating tab or similar to hold the surfaces together. Two bolts would be the most secure option of course, as OB has done. A bit more fiddly, and bolts can be lost, but in the end perhaps the best option.