Grinding RP to L70 with Blow Up II but the wall breach glitch isnt working when I tried, so here's what I'm doing with a Kuruma and using the train tunnel as shield:
* Start mission, park Kuruma somewhere near the train tunnel at Pillbox, opposite Apt 57.
* Get another car, go parking lot. Move the Banshee away and destroy the vehicles.
* Get into Banshee and drive back to the Kuruma, dont park Banshee too near the tunnel as it might get destroyed. At this point you should have 3 wanted stars.
* Quickly hop into Kuruma and drive into the train tunnel entrance, but not all the way in. Start shooting as u move in and lure the cops in.
* Soon police helis and swat teams will come and you'll have 5 wanted stars.
* Watch out for the trains approaching from your back on the right track facing train station. If the train is not moving, shoot it's driver.
* Kill cops for 10-15min. Then call Lester to remove wanted level (or drive into the tunnel and just wait).
* Drive Banshee to Simeon who is just around the corner. Ammunition store is just beside.
* 10k+ RP, $19200 - 25min run on Hard, Free Aim mode.