I've tried both a catalytic heater and a Propex heater in a Westy. Both
were 6000 btu and both did a fair job at 20-30 degrees.  They were more
effective if the poptop was not up.  I don't think a 2800 btu heater would
be adequate, based on what I've seen.  

The catalytic heater I've used was a vented model from Thermal Systems. 
Unvented heaters can sometimes cause condensation problems, but judicious
window-opening might circumvent this.  

Bill
www.geocities.com/yosemite/gorge/1706