I've heard back from Tecamp. Apparently some (nominally) 4 ohm cabs can be a little too low impedance and the power amp gets too warm and cuts out (though the case doesn't get all that hot), and there's a mod that Tecamp themselves do to add a fan by the ventilation slot (just glue it in with a silicone glue and solder up to a 12V supply from somewhere). They're supposed to be invoicing me and sending me a fan but I haven't heard from them yet. They sent me a photo from which I can make out that the fan is a Sunon MagLev 40x40x40mm fan, so it's probably a HA40201V4-0000-999, and they put a resistor in series with that, the value of which I don't know. If you're playing into an 8 ohm load, there's no need to worry.