Mike, my concern for someone like you is to combine strength, and power with balance and stability. Since you are doing more challenging terrain than the average recreational skier, you may require more strength power and endurance. But my suggestion would be to develop your strength in conjunctionwith stability training. Being more powerful than you are stable is one of the causes of injury.
Hopefully your gym, like most, have Stability balls. You can do the classic wal sit with the ball behind your shoulder blades. the diffference is that you make it dynamic rather than static. Start out going through full range of motion. Then go to 90 degrees of flexion, but do only partial extension movements.
To prevent ACL injuries, I strongly recommend hamstring bridges on the stability ball. Lie prone, feet about hip width apart. You will need a spotter to keep you in alignment. Gradually lift the spine into a bridge position. If you cannot go up that high, its okay to go halfway, Then, straighten you legs.Then bend them Come down from the bridge. Try again.
If your gym does not have stability balls, try doing things like performing squats and lunges while standing on the mats, rather than on the floor. You can also so one legged squats.
Gotta go teach. More later.