Here is a 3D printer:

Notice that it has a moving bed.

Here is the current Weedinator design:

The red circle indicates where the CNC / 3D printer machine is located - the machine frame is integral with the vehicle chassis. The design of the CNC machine will be different as we can not have a moving bed so the main flame thrower nozzle has to move along the X,Y and Z directions whereas normally it would just move in Y and Z and the bed would move in X. Can the 4 vehicle drive wheels can be used for X travel?

If so, then the CNC part would look more like this:And then, because we don't need so much travel in the Z axis, it would look more like this:

Or maybe it's a PNP machine like this:This one has a fixed bed and the needles move in 4 axes.