The Dubsta 2, especially the modded variant, is the white whale of Grand Theft Auto Online. It is an extremely rare spawn and has a number of specific requirements that need to be met before it appears.
When it comes to vehicle spawns in GTA Online, they are often not only tied to locations, but also to the time of day and to what vehicle you are currently driving. The hard part of this process is getting your first modified Dubsta 2, but after that it becomes easy.
We should forewarn you that the spawn rate of the vehicle is exceedingly low, so there's going to be a lot of waiting involved unless you're particularly fortunate.
The first step is to position yourself at the location marked on the map below, which you can also see in the video above. This is the best possible location to wait for a Modified Dubsta 2 spawn. You need to hunker down and get ready for the long haul. The target vehicle can spawn anytime between 8 AM and 12 AM, but is more likely to appear in the latter half of that span of time.
