Our evenings drop to 10º (at 7,000') frequently and I'll say that the lower radiator hose heater works ok but is ultimately not worth it. Personally, I'd return all that and put it towards a Webasto coolant heater (Espar is overly complicated with horrible directions and random wires) - I just put a Webasto in my 12HT Troopy and after 25 minutes of running, it fires right up with no smoke like it's been running all night. The lower radiator hose heater would run for 4+ hours and still have a very rough start. In the end $1000 to extend the life of your engine is worth it... PLUS you can't plug your hose heater in when/if you go camping in the winter.
Here's what I ordered and its pricing from Heatso.
Webasto Smart 7 Day Timer | 9029783A | 1 | $109.99 USD | $109.99 USD |
Webasto Thermo Top EVO 5 Diesel 12v (5.2 kW) Water Heater | 076-EA5-119 | 1 | $899.99 USD | $899.99 USD |