I was thinking that perhaps a new approach might be in order. The weak spot as I see it of the rapier motor is its high temperature burn and the chemistry which results in this. As you know Roger I was an supporter of APComposite fuels since I have a lot of experience in handling Ammonium Perchlorate, but it normally gives a hot burn which in turn give a higher thrust.
However it might be better to go for a lower temperature burn ie GN or Ammonium nitrate.
I was thinking of a sort of blend of the Scorpion system and the jetex system with a disposable type motor within a fire proof shell. Looking at what casing could be manufactured out of Titanium is available as thin wall tubes the most interesting being 15mm dia 0.5mm wall thickness and could form the basis for a jetex type motor. The rough calculations I have done would point to a thrust of 200-300mN being available from a low temperature reaction. so long as the design was kept simple the motor casing should not be difficult or expensive to make.