Sounds like the class t fuse for the inverter. I assume you have the Maganum Energy 2000 Inverter/Charger. That would be the recommended size for most installations.
Sportsmobile generally does not Fuse or Circuit Breaker the house battery ( or at least they haven't. I would not remove the Class T Fuse you have, but would recommend that you install another fuse or breaker close to the battery.
I have Class T Fuses in both locations, it is typically hard to find a circuit breaker that large with the proper protection requirements.
It is very difficult to blow that class t fuse. I am surprised that the inverter did not shut down before blowing that fuse. Also typically, I would say that the other 12 volt circuits should have been hooked to the other side of the fuse and thus had voltage. (The worse case inverter load would be 267 Amps)/
It can be common to use the Fuse Holder Terminal as busbar, so I would say that Sportsmobile wired your rig on the wrong side of the Class T Fuse.
[IMG]
[/IMG]
I would have expected that having the water heater and the tea pot would have at the most overloaded the inverter, causing a fault but not blowing the fuse. If wired on the wrong side any other 12 volt load would have been going through that fuse, also it possible that is why starting the van also had a effect.
Obviously just a theory, but when you go to have another fuse or circuit breaker installed you might want to have that checked out
-greg