I dry most of my puree every year and haven't had any issues so far. I use an Excalibur
dryer and do 2 cups puree per (lined) tray. To store I break or tear into pieces that will fit in a gallon freezer bag. I've found it's better to store this way and use a
coffee grinder to powder it as needed, since the powder tends to absorb humidity and form a solid mass in a jar. The dried puree stores for about 18 months, though it tends to get darker in color and loses some flavor after a year.
Also, to speed drying in the dehydrator, I put the puree in a fine mesh strainer (not lined with cloth or anything, but you could) and drain over a bowl for like 30 min to half an hour. I use the water to cook rice or in soups etc. The puree isn't quite as sweet and has more fiber, but it dries down a lot faster.
Even though the pumpkin is low-acid, the lack of moisture prevents growth of unwanted organisms.