Agreed. Although our Planar diesel heater is only rated for 2500 ft (without the altitude kit) we had ours running without issues for a couple weeks at 10.000ft. To increase the performance we installed a separate 1 gallon tank to be able to fill up with kerosene. Another reason for not plumbing into our fuel tank: this tank has been in place for 16 years... Did not want to tamper with it and end up with new hoses and such...Probably too late, but I would recommend feeding the Webasto/ESPAR gear from a dedicated 5 USG tank. This makes it much easier to use kerosine and there is a lot of anecdotal evidence that this prevents all manner of annoying problems with soot, especially at altitude - think western US or the altiplano.
It is nice to simply be plumbed into the main fuel tank, but I am going to be looking into adding a dedicated fuel tank for my Dual Top.
In the interim, remember the 20 minute burn every month.