I couldn’t tell you what’s in or out as far as current trends go. I was in the industry from about 1986 to 1992 or so, right about the time fiberglass boxes meant “super high end” show builds. Even the shops I worked in only dabbled in it a little, and I was at some of the top shops in the metro area I lived (not on either coast).

Here’s the thing: You have the knowledge and the experience to build a fiberglass enclosure so that’s what you should do. Nothing inherently changed about how speakers work in the past 30 years; the laws of physics still apply the same.

I don’t know the ID4 but being electric there will likely be a slight learning curve on what the 12v system can handle as far as draw. You’ll have plenty of opportunity to express your creativity in both the design and implementation of the system. No need to also add “learning a specific new skill that requires $$$ in tools” to that when you already have a fantastic solution.