Recently I bumped into the relaunched web pages of the highly esteemed HF Prediction pages of Space Weather Services from the Australian Bureau of Metereology :
On their sub-page "Internet Tools" they offer some excellent tools for HF propagation prediction which seemed to be tailored just to the needs of us listeners.
I wrote a short PDF (7 pages, 22 illustrations) about that, giving some examples. This paper also deals with multipath propagation, degrading even strong digital signals plus FAX. Among the Aussies' web page you will find a set of tools under "Digital HF Prediction", dealing perfectly with just this challenge.
Link to donwload the PDF: