Find a car called Scrubber[saintsrow.wikia.com]. Its respawn chance is 50% and you can find one anywhere in the city. The Zombie variant spawns on Arapice Island only in Survival 26. It has with spikes on the front and sides, boarded up windows, the scrubbers replaced with saw blades. It can be saved in the Garage via Rim Jobs, after failing the Survival, and can be customised normally. Also the normal scrubbers with the brushes that you can find around Steelport (mostly during night time) can be upgraded to have blades and spikes etc.

Find a Rim Jobs[saintsrow.wikia.com] and customize your car to your hearts' desire. You'll find that this scrubber isnt such inocent car.

UNLEASH HELL ON STEELPORT!

This section of the guide is only for people who own the GENKI BOWL VII DLC !!
There`s also another way to obtain a decent 'monster truck'. The answer is Yarnie[saintsrow.wikia.com]
Yarnie is a giant ball of yarn which rolls around. It has a build-in Shockwave weapon which deals damage in a large area and allows the vehicle to jump. Because of its size, Yarnie can not be stored in garages, nor modified at Rim Jobs.

• Yarnie is used in the Sexy Kitten Yarngasm activity in the Genkibowl VII DLC.
  
  
• When the activity is complete, Yarnie becomes available as a Homie Vehicle Delivery service.
  In the activity Yarnie has nitrous and the Shockwave weapon needs to be charged by causing damage. Outside of the activity, nitrous can not be obtained and the weapon does not need to be charged.