Is the walls cover with dry wall ? What about the celling? is there one in there? If not i would do some insulation first. Styrofoam insulation is the best and easiest to do then fiberglass secound if you dont want to or dont have the cash for dry wall then hang some thick contactor grade plastic over top of it the insulation then your keroseen heater will work just fine..
Dont forget to do the ceiling to as this is were most of your heat will escape..