As noted above, many of the so-called IEDs are 155 mm (US/NATO) or 152 mm (Soviet/Russian) artillery shells and are only "improvised" because they are being used in a manner for which they were not intended, that is, to be fired out of the barrel of an artillery piece. The most vulnerable point on any vehicle - tanks included - is the belly. Detonate a 155 mm HE (high-explosive round) under an M113 (an armored - but not much - personnel carrier) and it is going to be destroyed. Combat - whether "low" or "high intensity" - is dangerous, even in armored vehicles. It is much more so dismounted (on foot) in an urban environment; such is the nature of so-called Fourth Generation Warfare.
It's not an open vehicle like a jeep. But it still seems to have large open windows in the side, which is a vulnerability even for small arms. Bulletproof glass might help. What if the enemy then launches an RPG their way? Would light armour and bulletproof glass make a difference for the men? Would they still be alive? Would they largely escape injury? Would they be dead either way?