Aperiodic (literally "not regular") in philosophy is similar to transmission lines in that the goal is to tame impedance peaks so that the speaker, at least from an electrical POV, does not appear to be in a traditional enclosure at all. As an example of what an ideal aperiodic enclosure should behave like, you can imagine a subwoofer with an extremely low natural resonance in a 1 cubic foot enclosure with a door on the back. As you play higher frequencies, the door is all the way shut, but decreasing in frequency the door opens more and more, so that any measurement of impedance would be riding somewhere on the tail of the resonance spike without ever reaching a peak. The attached picture demonstrates this, in that as you get lower in frequency and the fb peak is pushed lower and lower the impedance stays the same (green line). In reality this isn't possible because it relies on a speaker with no inherent physical properties. There are theoretically other forms of resonance shifting that would make for non-regular behavior; you could even make the same kind of setup but have the door open a random amount for every frequency. This would be aperiodic as well because the impedance graph would be all over the place.
Aside from the classical definition, when talking about real speakers with real mass, aperiodic works in a similar manner, with the ultimate result much like that of the adjustable door, but you still get the characteristic of a sealed enclosure. The goal is to get the characteristic impedance curve of a larger enclosure when the speaker is in a much smaller enclosure than would normally be necessary to get that response. You can do this with an acoustically resistive membrane, but the problem lies in the fact that most membranes have a tendency to act like the randomly opening door. If you just guess on the amount of stuffing you need, you end up with a peaky and wobbly impedance response that looks more like a really leaky sealed enclosure. So to get it sounding right takes a LOT of experimentation, and even then you can't guarantee that you'll ever get a response that sounds better than another type of regular alignment like a simple sealed or vented enclosure.
So since the end goal of going aperiodic is to make the enclosure seem larger than it really is, there's a much more simple answer: use a driver with a slightly lower QTC then you want to end up with and put it in an IB configuration. This shifts resonance down, increasing low end, and assuming the opening at the rear is large enough to not cause helmholtz effects, there's still a slight underdamping effect. None of this is to say you can't add some form of stuffing to the enclosure, in fact it's a good idea for (if nothing else) keeping outside noise from entering the enclosure and exciting the speaker cones.
I don't think stuffing a ton of 15"S in an IB config in a truck is necessarily a good idea, but it will work a hell of a lot better than trying to mess with aperiodic damping.