Amabee, Now that you mentioned the vinyl windows, that may have been the main concern with the warning label, and not the tent ends in the pop up.
The earliest I would go camping is mid April, so probably for me, an emergency blanket under the mattress, my little portable ceramic heater, a sleeping bag, and the furnace, and I will probably be fine.
For us, the $300 cost of the heated pads wouldn't make sense, but for folks who go more often in the cold weather it seems like a great idea.
I remember years ago we would go in early to mid April in a tent with nothing but the cots, sleeping bags, and a couple of comforters. I remember being warm when I was wrapped up in the bag, but stepping on the ice cold tent floor was never fun.