When fighting GRIM he will sometimes turn invisible. When he's invisible you will not be able to find him on you map. But watch where mason's sidekick aims because that's where he'll be.
A quick way to get lots of dough, get like armor level 2, have a strong car and then follow a tornado and u'll be loaded after it passes
NOTE: for better money, get a RIOT to go in the hurricane. i got about 20,000 from one tornado.
Get new cars
You can get all the gang cars in a level and some other cool cars if you do the side missions
To find the rigg truck boxes there are two by the power station and one if you turn right down the road form the power station you start looking behind the buildings you will find a fang ,rigg box.
And if you get in a world of hurt and nos runs out go to your garage and come out again, you will be refilled.