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To turn the insurgent pick-up into a personal vehicle it needs to be upgraded to the insurgent pick up custom. The upgrade cost 202500
Unfortunately this cannot be done at a regular mod shop. Instead a “vehicle workshop” is needed. I used the one in the avenger but according to GTA wikia you can also used the one in the mobile operations laboratory (though someone edited my post claiming the opposite). Unfortunately it seems you cant use a friends workshop, only your own.
As for upgrading the Insurgent Pick up into Insurgent Pick up Custom you can also modify it at the Mobile Operation Center (MOC) with a Vehicle Workshop purchased. But in order to purchase the MOC you need to own a Bunker. Pretty much the same goes for the Avenger; I believe you need to own a Research Facility and you also need to equip the Avenger with a Vehicle Workshop. I guess it all comes down to the price, whether you will find a Bunker cheaper than the Facility or vice-versa. To be honest it is best to wait for sales in the game. They often offer great deals.
Grand Theft Auto Online
The Insurgent Pick-Up Custom is a modifiable variant of the Insurgent Pick-Up, where it retains the exact same design and properties as the regular Insurgent Pick-Up, except that a tow-hitch is added, able to tow another players Anti-Aircraft Trailer. The vehicle can be modified with an array of visual modifications, being armor plates, liveries and respray colors.
Color distribution is the same as its Pegasus equivalent, and retains the same wheel design and color as the aforementioned vehicle and the Insurgent.
Similar to the Pegasus version, the vehicle is equipped with the same machine gun turret that resembles a Browning M2HB .50 caliber machine gun, but can be replaced with a three-barreled .50 caliber Minigun resembling a GAU-19 gatling gun.
To get your HVY Insurgent Pick-Up Custom you have to buy the HVY Insurgent Pick-Up and get the transformation at one of these vehicle workshop : Avenger or Mobile Operations Center. The cost for the transformations is $ 202 500. The total cost including the purchase of the HVY Insurgent Pick-Up and the transformation is $ 1 552 500 to $ 1 997 500. Your mechanic will deliver the HVY Insurgent Pick-Up Custom close to where you are by contacting him with your phone.
How do I get the insurgent pick-up in my garage?
Can you sell insurgent pickup custom?