This is my first GTA mod.
What I have done is made the journey enterable, lowered it, and cut out the roof and windows so you can go inside it and shoot out at pedestrians.
You can also climb into one while a ped is driving it (while they're stopped) and hitch a ride!
I removed the 3 rear-most windows and the whole section of the roof behind the cab, I also edited the col file so that you can jump in through the top or walk in through the side, the only bugs I have noticed are that it scratches on the ground when going uphill or on slopes, and that you walk in slightly beside the door.
I have included a line of code for the handling.cfg so that the journey goes faster!