We take great care in insulating the entire building envelope. Your floor joists and rim joists need to be insulated too. Ensuring that these two areas have no voids will prevent many future problems including cold floors or drafts.
Although you could install fibreglass batts yourself in the floor joists, often times the friction fit installation of fibreglass batts and Roxul will leave voids and gaps that may or may not be visible to the eye. It has been demonstrated that a near perfect installation of batt insulation will leave approximately 5% in void areas that will lead to heat loss, convection and possible moisture problems.
Reduce these risks any problems by having a professional install loose blown insulation in every area of your house, including the floor joists and rim joists.