I don't know if anyone else can testify to this, but I own a MIA SVT-410 HLF (circa 2000-ish) that's missing enough tolex now to know that it is most definitely built from some sort of wafer/fiber board. Upon discovering this, I took out a speaker to find an assortment of lumber inside. The baffle is built from quality plywood. However, from what I remember, all the internal bracing looks like MDF or something similar. A buddy of mine has the same cabinet (produced a year or to later), and we found the same results. Anyways, I've been doubting the QC and material choice of Ampeg for a while now.
With that said, after almost 8 years, it works fine and still sounds great. I just definitely thought I bought a plywood cabinet (thats what I was told and read), not something I would feel like I'd have to take unnecessary measures to protect... It's hard trying to baby a 110 lb. cabinet out of that back of an SUV by yourself...
Well. again maybe I just WANT to love Ampeg-
I bought my SVT-48HE about 5 years ago- it's literally been around the country, and then the world with me, prety close to it anyway.
First thing I did was buy an excellent Tuki cover, then a flight case when I went took it overseas. Barely has a scratch on it.
I'm always careful when transporting my stuff, and try to keep things under control when it's on a stage.
(And it's been in Clubs ranging from first-cabin to...
DUCK! Here comes another beer bottle!

)
My SVT-15E is about a year old, still SLM, but a later build than the 4x8- (speakon jack, etc.)
Seems solid to me. The website claims they're made of baltic Birch IIRC, maybe that's changed, they haven't updated the site.
I would wager that like most companies Ampeg/LOUD uses Eminence-designed & built drivers, of course I may be mistaken. But I'd be interested in knowing if in fact, there has been a spec change.
Same with the cabinets themselves. Only an "insider" could say whether or not LOUD has started using different woods, or has gone to MDF or OSB or whatever. Maybe Mr. Tiers has some knowledge.
I'm not about to take off the tolex on my cabinets, and btw, the tolex seems to be as well-applied and as durable a grade as any other tolex-covered cab.
I think that with reasonable care, the Ampeg cabs will be as durable as needed. certainly able to hold up.
My main criteria would be their sound, and I'm really not certain that the new builds from Overseas haven't made the grade in that respect.
Like I said- here's hoping that Ampeg makes it all work- for them and us.