Making a really big and heavy thing like this should be easy Jbeam-wise because you don't run into problems with stiffness to weight ratio or clipping due to the sheer size and weight. (Unless you want a ton of detachable parts but this doesn't have them.) You just need a 3D model and basic Jbeam knowledge I guess. So you could make it yourself.
TL;DR: It's a meshslap --- Post updated --- Size up the T-Series semi truck, then do the meshslap. --- Post updated --- Size up the T-Series semi truck, then do the meshslap.
Nah you can actually see that the Jbeam fits the shape in other videos. I wonder how this one youtuber always gets all the cool private mods, like the non-meshslap Cybertruck, the Hummer, all the different semi trucks, trains, and now this thing.