I think there is a mismatch between the "Heavy rescue" vehicle, the new SAR and technical equipment and the way we have used the heavy rescue vehicle since the beginning of the game.
According to the missions where it is needed in the game, the heavy rescue vehicle would often be named a "USAR" truck in several fire departments. In any case, it should carry SAR and technical rescue equipment by default and we shouldn't have to add this equipment to it.
SAR and technical rescue equipment should be allowed in fire engines, trucks, fly cars, utility units or ems rescues for instance, or in any vehicle if you want to simplify the game. But please, consider changing the name of the heavy rescue or at least have SAR and technical rescue equipment by default in it, like in real life.