The kits we have here use either the Mojotone chassis or the Weber chassis. It depends on how quick we need to restock.
On both of these, there are a few holes that need to be drilled to mount the OT and the fiberboard. Depending on output configuration and the impedance switch, you may need to drill those as well. I find the Weber chassis to be a bit more robust and the predrilled holes require less “customization”, though a few holes may still be necessary.