Ok.. My repair shop is a warranty center for Mr Heater / Heatstar and we do out-of-warranty service on all other brands as well.
It' perfectly fine to run diesel or heating oil in your kerosene forced-air heater it shouldn't cause any problems. Never ever, EVER use gasoline for obvious reasons.
Diesel may not burn as clean as kerosene so you might want to run some "Meeco Red Devil" or similar oil furnace soot remover every ten tanks of fuel or so just to clean the burner out a bit. You may need to open the heater and clean the soot from the cad cell lens every few years as well but you'd probably have to do that with kerosene too.
If stuff goes bad with the heater, it's usually lack of maintenance or a faulty operator.
Propane heaters are the suck for anything but heating an open building. I know a lot of contractors that won't use them because of the amount of condensation that they create. For some reason you get a lot of moisture in the air when you burn propane, not so much with fuel oil.
Good luck with your heater, don't run it near anything flammable or tip it over. If you do, you'll need to answer to Woody.
Shawn
P.S. If there's a marina near you, you can probably get kerosene from the pump. If not, open the yellow pages and look for heating oil. It's cheaper and it works fine.