I have a Marshall 4x12 bottom that I loaded 2 V30's and 2 G12t-75's in an X pattern, soldered everything with heavy guage wire and along with making sure the screws were tighter than shit I ran silicone beads on the speakers and the back panel. I did all this as an experiement and it is a fucking monster sounding cab. LoL I don't know if the wiring and the silicone are why or just one or the other but it's been with me since 92 or some shit, always getting the job done.
The tightened cab sure beefed up! It's amazing how much gets lost from that air leaking out the back.