I'd still put an air exchanger in the furnace, and put a bypass to it. That way when you're leaving for a week, you can open the bypass and allow the propane to keep the lines warm. When I leave for a a few days in the dead of winter, I turn off the blower on the stove and let the propane heat the water. I got back last winter and it was about 0 degrees outside temp, but my water was 120 degrees. It seems counter-intuitive, while actually making sense, that the colder the outside temp is the warmer the propane keeps the stove water, because the more often the propane furnace kicks on in the house to keep it at a set temp. Right now, with the outside temps in the 30s, the water temp from the propane furnace is at about 70-80 tops.
Having the exchanger in the furnace with a bypass also gives you the option of burning extra wood from time to time to save on propane to heat the whole house and not just the basement.
I'm guessing you'd want to run to DHW, then to the exchanger/bypass, then to the in-floors.