Electric furnaces and gas furnace are equally efficient in mobile homes, assuming you are making an equal comparison. The more expensive the furnace, the more efficient it is. For just a few hundred dollars, you can increase the efficiency of both gas and electric furnaces from 80% efficiency to 90% efficiency.
Another factor to consider are that electric furnaces are cheaper to install, but more expensive to run. You need to decide whether this is for the short term or long term. If it is long term, then go with the gas furnace. Although it has higher initial costs, gas charges are cheaper on a per unit basis.