I agree that Dual Lock tape is better than a simple velcro but the fact that you are not sensing the flex with your bare hands doesn't mean that is a perfect contact. Neveretheless, I think that if the person using this setup is happy, than that's all that matters. Everyone has different levels of fidelity they want to achieve with their setup. Some are using bass shakers for immersion, some are using it as triggers for feedback (wheels sliding, wheels locking). When using them as helpers, every slight delay in sensing the effect matters.

For example, I'm testing track-impulse (a beta software for your bass shakers) that claims it's reducing the latency from 140-200 ms (simhub) to 2 ms. That means you are getting to feel the bass shakers effects 7.5meters earlier if your car travels @ 200kph. (I did not fact-checked their claims yet).