Hi Perp
Yes, just being a beneficiary of a trust means you have an interest in the trust assets, an equitable interest and on this basis a caveat could be lodged. The authority for this is Paul A Davies (Australia) P/L (in liq.) v Davies [1983] 1 NSWLR 440
I wouldn't say any beneficiary has a claim on trust property (, but they do have the right to be considered, at least, by the trustee when they make the decision on who to distribute to.