My experience has been that RV antifreeze is not the best for winterizing. A while back I did a test on some rv antifreeze from Walmart and it froze solid and bulged the jug. It for surely would have popped my heat exchanger. What I have found is that windshield washer fluid is best. It always stays in liquid form. I get mine from Napa. It's also cheaper than Rv antifreeze. I also recycle my windshield washer fluid by putting it back into jugs and using it in my pickup. I'll try and find my pictures of the froze jugs of antifreeze and post later.
I was curious as to which one was better for winterizing. I went to RV Antifreeze after handling regular antifreeze was to much of a pain to dispose of. What I discovered really surprised me. It's -10°F here and I set these jugs out overnight. The Super Tech I bought at Walmart for around $2.50...
I have read all about the RV products freezing and expanding but supposedly not having the burst pressure to harm anything.
Not sure I am willing to take the chance. I'm liking the windshield washer fluid more and more.