Block heater couldn't hurt. I'm a fan of the pulsating tank-type heaters that install in the heater hose. They actively circulate water through the block, instead of using radiant or gravity to spread heat, like a freeze plug heater.

In theory, you shouldn't be using a lot of fuel, since it should only take 15-20 minutes for the engine to reach normal operating temp.

You could always try the old "put a piece of cardboard in front of the grill trick" to block or partially block the airflow through the radiator, to make it warmer.

You won't find one that operates off the battery. They use too many watts. At least 500. Dipstick heaters are pretty worthless too.