It's pretty easy to remove it all. Get underneath and disconnect the hoses first. You can take the fuel line and all just use something to pinch off the fuel line coming out of your fuel tank. You probably won't even need an install kit.
My answer would be the same in either Van. When I had a d2 and it dropped well below freezing I would use heavy curtains in front of and behind my bed. That made a big difference. If I had a d2 already I would probably use it though. I never regretted for one minute upgrading to a 4.
At 32 degrees it will work well at 10 degrees it will run full blast constantly, burning more fuel and wearing out parts faster. It most likely won't get your van to the 70. For a few hundred extra get the d4, you'll be happy you did.
I would rather spend extra on a unit that will keep me comfy and sleeping in my boxers at 0 degrees than save a few bucks on one that works but is blasting on high all night to keep it at 68 in 0 degrees.
When there is an oversupply of vans it's easy for carriers to turn away older vehicles. They can choose to be picky when they get five or ten calls a day asking if they are putting on vans. It's the same old supply and demand we have talked about for years