Just a brief update - I went for the option of tweaking the Jakob Winter JW 2195 CA, compressing the polystyrene foam with a tool handle wherever it was touching the keys / cups, just enough that they were no longer under pressure. Laying a ribbon on the relevant areas, then closing the case and drawing it out, allowed me to be sure that there's now no pressure where there shouldn't be. The instrument is snugly and firmly held by the bell and main tube, with no movement at all, in a compact, waterproof, "Thermoshock" rigid case with which I can cycle. Altogether a very satisfactory solution.
Thanks all for your advice, cautions and suggestions. Maybe I should submit these notes to the people compiling the "Definitive List"?
@sizzzzler - may I ask what solution you ended up with? Did you end up tweaking a case to fit?
As my Forum name suggest, I play the viola da gamba - these do not come in standard sizes, unlike cellos, violins etc. Most cases are customer made - certainly for the luthier made instruments. The main company that does that is Kingham - I'm pretty sure they make cases for wind and brass instruments as well - worth a chat? Last time I enquired, a case for a tenor viol, which is the size of a guitar, was around £400
One of my SML tenors in its Protec case came off my motorcycle at speed. Fortunately it just landed and skidded down the road so it wasnt too drastic a test. Other than a few scuff marks there was no damage