My recommendation: Leave it off. If takes so long to get the oil up to temp, any amount of running it will just introduce more condensation to the oil, which is eventually what causes the oil form acids. Good oils have buffers to reduce this affect, but that will depend on brand and current oil age.
Do top off the fuel tank. You don't want dead space in there for long term storage. If you do drive, try to get a 20 minute trip in at least.
Shore power is fine. Your converter should keep it from over charging (but might not hurt to do a voltage check to verify). If you have parallel switch (also called emergency start) , this will let the converter keep the starting battery topped off as well. If you don't have this feature, then the best option IMO is to fully charge the battery, then disconnect it.
2000 E450 dually V10 wagon