We have three different systems of keeping ourselves warm in Honu.
When the temperature drops but still above 45 degrees Fahrenheit, we use a small portable electric heating unit called "My Heat" advertised as offering safe, ceramic warmth. It is a very small unit with 200 watts and only single on and off setting. But it is adequate to keep the interior of Honu warm and cozy. This unit is especially useful when we have no external electrical hook-up and only rely on our batteries.
The second portable heating unit we use has 5 different temperature setting modes; 60, 65, 70, 75 and 80 degrees Fahrenheit. We use this when we have external electrical hook-up and when the temperature drops below 45 degrees Fahrenheit.
Aloha -- Cathi