The Rumpo Custom is a heavily customized variant of the Rumpo, which, while retaining its front fascia, the rest of the bodywork was severely changed. The Rumpo Custom features modifications similar to the Merryweather version of the Mesa. The significant changes of the Rumpo Custom over the standard model is that the rear doors are replaced by two sliding doors on the sides, in a similar manner to the Minivan Custom and Moonbeam, which allows passengers to make use of full-sized weapons, such as assault rifles and light machine guns.
The Rumpo Custom performs much better than the standard model, since the off-road tires, combined with its high suspension, makes it much easier to drive over uneven terrains. The vehicle features bullet-resistant glass panes, giving the occupants temporary protection from gunfire. A disadvantage of the Rumpo Custom is its heightened suspension; even with upgraded suspension, it is prone to tip over when cornering at high speed.