Hi
These trestles look flimsy in the extreme and totally dependent on being placed on a very sound foundation (yard). Where I am on a gravel surface these would be totally unsuitable.
My 26 'rascal' sits on a galvanised steel table framed base with 2 cross supports with timber bearers and shaped wedges, designed by a structural engineer so probably well over engineered.
For ease of access the legs are not high enough for full keel drop, but this winter I will dig a small hole under the keel to allow for this as I want to adjust the keel guides a bit.
As for being demountable, it all bolts together, but would need a lorry to carry the individual parts.
I can measure the steel sections if you are interested.
Philip