Here are some places to do the jumps.
Accelerate as fast as possible down this road, and just drive straight towards the building. It's really easy to get Triple Insanes, and pretty easy to get Perfect Triple Insanes, it just may take a few tries. It's a pretty fun spot, with a new Banshee waiting nearby if you blow up your car.
Basically, drive as fast as you can towards this pole and hit it. There are three roads you can take coming to it, but all work fairly well. It's a little harder to get a Triple Insane, but Double Insanes come a little easier.