Wave 3 will be fine unless you camp in areas below 20 degrees F. We have the 3 in our 10 foot Avion, and is our only source of heat. When we camped in the Mainland of Alaska in November, we were glad to find a Campground still open, even though they only offered electricity. This allowed us to supplement the heat with an electric heater, that took our camper from -9 F to about 60 F in less than an hour (wave 3 and electric 1500 watt heater together) and kept us at about 60 all night! and it dipped to -14 F....
Living in Alaska, I almost wish I went with a Wave 6, but when we put 4 or 5 of us in the camper, body heat helps heat up the rest of the way.
:) ;-)
Hopefully this helps out! Also if you camp in Cold Weather, pick up some of the aluminum faced bubble-wrap insulation, and line cupboards, place under mattresses, and I use Metal "Duct Tape" to put it over the windows which was the only way for us to hold any heat at all in our sub-zero Thanksgiving.
Good Luck!
Garry in Kodiak, AK