I'd go with an Atrium door instead.
The reason why is the threshold is far stronger and I've never once been able to get a Pella or Anderson rep to come look at windows or doors my customers are having trouble with. Home Depot sells Atrium.
I also strongly suggest while the door is out you add what's called a jam sill. It will stop any water from getting in around or under the door and taking out the subfloor.
http://www.jamsill.com/
Pay special attention to the flashing under and around the door for a leak free install.
Make sure the threshold is fully supported on the outside so it can not twist and cause a leak.
A piece of 1 X 6 vinyl lumber attached with SS trim head screws works great.