The Natural Philosopher wrote:
Building in straw should be lioke building in blockwork.
And I should think expanding foam to hold door and window frames in
woould be appropiate.

Hold in with long wooden staves driven into the bales.

Not sure how to arrange for a wterproof skin though - breathable
membrane, air gap, metal lathe and render maybe?

Blue plastic held down with baler twine.

Owain