This is excellent and exactly what I was looking for!

I just want to point out a few things that I've missed in the critique that I should have pointed out then.

• First thing I didn't mention in the critique is that the lines shouldn't be arbitrarily decided. This is so that every line is able to be replicated on to the 3D construction which you've done for the most part. However if we take a look at this I've marked out some points which can't be easily replicated onto a 3d construction. Here I've done a step by step of how I would have defined the window bar thing so that I can replicate it onto the construction. I would do the same for all the other points as well so that they can be easily replicable.

• The second thing is about curves which should be kept as a straight line before deciding to curve it. I can see that you've faintly done this in some areas but in others I think you've relied more on observation (the same areas I've marked above). If possible try not to draw curves at all and instead draw a lot of subtly changing lines that closely resemble the curve. This is again for the sake of replicability onto the 3d construction. This is especially hard because vehicles are all about very precise subtly changing curves and so it's critical that they are defined as straight lines, even if the subject at the end comes out box-like you can always add curves after you've finished construction.

• The third thing is to always contain the whole vehicle inside the bounding box and to not extend a portion of it outside of it like you've done here and would instead add another circle to both ends of where you want to extend, the downside of doing this is that you're left with a lot of empty space. To combat this, what I did was I actually started the base of the construction about 1/3 inside of the other wheel which I've highlighted here . After I drew the base I then extended the line away from the vanishing point to place the wheels, like what you've done for the side mirrors except you've done it in the middle of the construction which could potentially undermine it. So even if there is a lot of empty space you can still start the construction with the core part of the vehicle which in your case would be the wheels + hull and then you would add the side mirrors. Now this is obviously extreme for your case where the mirrors only go out 1/8th and I would probably just do what you did. But the reason we do this is so the construction isn't undermined.

Finally I'll address your points.

• First, you are absolutely right in that there is really no need to go beyond 1/3 for a plane which I also realised in some of my later constructions. But it's really up to you how far you want to take them. I've seen people go up to 1/64 or 1/32 (If you're curious what that looks like you can look at this persons work or this one both demonstrate an extreme amount of patience). But what matters is how far you feel you should take it. If you don't see a reason in going above further than 1/3 then there's no need to.

• Proportional mistakes occur and you don't need to worry about the believability of the vehicle. If you've seen the above examples some of theirs look extremely stretched / disproportionate which is absolutely fine and to be expected because at the end of the day these are just exercises to train our spatial reasoning and will not look good. This might be confusing since you've previously done these and they look good partly because you've fixed it while drawing it. By deciding everything before hand and sticking to that plan no matter the outcome we can confront our mistakes directly and see where we went wrong so that next time we can do better.

Anyway congrats on completing the challenge and now I can more confidently say that you've completed drawabox! Also if anything was unclear or you have further questions don't hesitate to ask!