The three bonus objectives are:
- Complete the challenge at night.
- Reach the destination withh both A-3151 Jeeps
- Reach every watchpoint
When given the option at the start, change the time to night.
Attach to the second Jeep with the winch and make sure it is in drive mode. You don't need to reach every watchpoint with both Jeeps, just the final destination, but I would highly recommend you keep both attached. They flip easily so having a second Jeep to turn them over is helpful.
Drive as far West as possible. You'll reach the edge of the map. If you look South, you can see the watchpoint across the water. Drive along the shore to reach Watchpoint 1/3. The map will clear and reveal a small road leading to the next watchpoint, halfway between the previous one and the final destination. Drive up this road for Watchpoint 2/3. A new road will be revealed which goes either to the final destination or the last waypoint. At the intersection, go left (East) down the mountain. Slowly make your way down until you reach Watchpoint 3/3. Now just back track the way you came down to get back on the road, and drive to the Final Destination.