While at The Battery Technology Show in Coventry today I crossed some ideal material on the 3M stand. Polyurethane Foam good to line the inside of the metal case. Might see if I can find some online and have a quick try of it to replace the rubber. At the moment the rubber lining is doing well but I find it hard to manoeuvre the cells in the case when aligning and constructing it. The foam seemed less grippy.