Re: an auxiliary heater - don't most/all Toyota engines come with a block heater slot?
You then buy a block heater, slot it into the block (no fiddlin' with coolant) and then wire it in to an external mains powered socket. On a timer if you're really slick.
The other option is to fit an inline coolant heater into the lower radiator hose which means draining most of the coolant, refilling and bleeding.
I'm not sure how effective a block heater is vs an coolant heater tho.
For the few really cold mornings we get in Blighty I'm not convinced it's worth the hassle, although I get very tempted each year...