Hello Kristin,
Thanks for stopping by the Disney Parks Moms Panel! I think making a seat cover is a fantastic idea; it will certainly set your stroller apart from the many other strollers that are rented. Unfortunately, I am unable to provide you with the dimensions of the
Double Strollers, there is only a recommended weight capacity of 100 pounds listed on the
Walt Disney World Resort website.
I have rented them in the past when my children were younger and they found them to be uncomfortable not only because of the plastic, but also because they do not recline. Another thing to consider is that the strollers need to be returned upon exiting the Parks and Downtown Disney Area so if your child is asleep; it's not an ideal situation. Carrying an exhausted child onto a bus and through the halls of your Resort to get back to your room is, pardon the pun, "no day in the Park."
I suggest renting a stroller through Kingdomstrollers.com. The strollers are delivered to and picked up from your Resort hotel. All you have to do is choose your stroller, give them your Resort information and the time of delivery and pick up you prefer, and they do the rest for you. If you would still like to make a cover for the stroller then I am sure they would be able to provide you with any sizing information you may need.
I hope this information helps!
Magical Wishes,
Susan