I like the one Jeff posted, cheaper and a built in thermostat....plus,
you really don't need any longer rope because the heat is going
to go up anyway, so maybe wrapping half the trunk and leaving
space to let the air rise.....one thing I would do(even if you have to
put the plug in up high)is to have the thermostat near the top if possible
so it isn't frying the top of the plant....although maybe you leave it open so
you would want to have your remote sensor(for temps)
near the top(meristem).