Use the Optimum Weight function in RASAero II (see Pages 92-93 in the RASAero II Users Manual).
Note from the RASAero II Users Manual:
"Note that for many larger high power rockets, and sounding rockets, the optimum weight is typically the lowest possible weight of the rocket. RASAero II will stop the optimum weight flight simulation trajectory iterations once the weight has gotten down to the motor loaded weight from the rasp.eng file, i.e., there is no weight left for the rocket airframe and other rocket systems."
Once the Optimum Weight is determined, you can do individual RASAero II runs at different weights to make the flight simulation plots and get a look at what is being traded in terms of max velocity and altitude gained during coast.
You can also try different weights with different levels of wind to look a weathercocking off the launch rail, and trajectory effects.
Also, with the Rogers Modified Barrowman Method (Page 36 of the Users Manual), you can look at the forward movement of the Center of Pressure (CP) with wind. (CP is fixed with angle of attack if the default Barrowman Method is used.)
Chuck Rogers
Rogers Aeroscience