I took some reference shots of the original model from Half Life 2 and I modeled the main volumes and the wheels. Just using the basic modeling tools, piece after piece, I assembled a replica of the main volumes of the APC (Fig.02). If you break up any complex model into small areas and you focus on each piece one per time, there is nothing too complex to achieve. Modeling is pretty much all about that.
For the smaller, realistic details I just had to model them as they were in the reference photos I'd chosen. For other elements, such as the rims, the headlights or the roof, I tried different solutions. It was a trial and error method, and I discarded and remodeled them until I was happy (Fig.03). In cases like this, I use any method that will allow me to save time. Usually I take a screenshot of my viewport in a perspective or ortho view and do a quick paintover in Photoshop, so I can understand if what I have in mind works or not.
Another little trick that may not be obvious: over the years I've created a database of nuts, bolts and common, simple objects, with proper UVs. I selected some of these and I used them all around the model. During the UV work and texture work, I knew this would pay off a lot (Fig.04).
As I model, and the number of my objects grows, I always take some time to keep my scene organized and tidy. Giving proper names to objects, with a proper prefix, and creating some layers to quickly hide sets of objects saves a lot of time, and headaches, in the long run. Especially, if you have to pass your work to someone else! It's a good habit to keep your scenes clean (Fig.05).