I've done both Blender and GIMP-only methods and TBH the GIMP method is nice in that you are stuck with one camera shot decided in advance. Eventually in full 3D I start fiddling with camera angles think about all the animation possibilities and it's downhill from there, time-wise. :-)

Though I have also found that it's sometimes nice to block things out with Blender so that the camera perspective is easy to work out quickly and the main shape lines are all blocked in...