Help!!  I am needing to heat a 22x30 garage with minimal insulation
and a ridge vent in the roof(stands alone in back yard  unattached
from the house.

I tried one of those wall mount 30k btu propane heaters last year and
it didn't get the job done much below 20 degrees.  I sold it and now
need a REAL heater.  Don't have a natural gas line to the garage and
would like to not have to bury one, so that pretty much leaves me to
electricity(have a 220v line in there), kerosene, and propane too
heat this bad boy.

So far, I've found a $480 mount in the rafters propane heater( with a
stainless exhaust system that adds another $130 to the cost) that
throws 45k btu.

The other option is going to a kerosene fired Reddy heater or
something like that, but kerosene is higher than diesel fuel these
days and I would likely have to mount a CO detector in the garage if
I bought one of these, but its portability would be a plus.  They
come in sizes from 55k btu to 175 k btu($200-420), and they drink
about a gallon per hour of usage.  The other option is to get the
propane-fired version of the Reddy heater, but it wouldn't be as
portable if I used the tall propane tanks stationed outside the
garage.  they also run in the 55k to 125k capacity range, but the
125k is only $200.

The initial cost is important, but I'm more concerned about what
either of these systems will cost me to run when it gets below 20 degrees.

Is propane substantially cheaper to use than the kerosene?  Since the
30k btu unit didn't do the trick, any guess as to how high I need to
go?  the attic area oft his garage is substantial, although the roof
pitch is moderate at best.  I think by cracking either the walk in
door or raising the bottom of the double garage door, I should get
enough ventilation with the heat escaping through the ridge vent, but
any help or experience from the list would be greatly
appreciated.  BTW, I would be working on my Vanagon in this garage(RVC)

Thanks
DM&FS