Full stochastic crossover ...can anyone recommend how to write as a scan?

On the Advanced Scan page, you can select Full K and Full D from the Technical Indicators drop down in the Scan Builder section. That will put those two indicators in the Scan Criteria window.

You then have to edit the inserted text so K and D are on one line - K first, then D, separated by the "x" (cross above) operator.

You should probably also add something to indicate the stocks you are interested in - maybe an exchange or a group or a market cap level so you get a more manageable number of hits.

Then do Check Syntax to correct any errors, then run the scan.

Click on the Instructions link at the bottom left of the page for an intro and links on syntax and so on.

If you get stuck, post what you have.