I wouldn't worry too much about burn-in. Even drastic burn-in on the VFD has little effect to the image when the display is running (although it can be quite visible with the display switched off).

We have an early Mk.1 in a display cabinet which has been switched on with nothing but the empeg logo on the screen for a large proportion of the last 12 months. I guess it's about time to invert the display in software and leave it running for another year to even out the phospher burn!

Rob