Give your pumpkins a bath in 10 parts water to 1 part bleach
Wash tub, Water, Bleach
Soak them stem side down to keep them from bobbing up out of the water
After letting them sit for 10 minutes or so, dry them off and then buff with Vaseline and a soft cloth to make them shiny.
Petroleum jelly
Video
Notes
If you notice that one of the pumpkins or gourds gets a gouge in the skin, be sure to rewash and seal with Vaseline again. You don't want any bacteria getting inside and turning them to mush.The same thing goes for the stems if one gets broken off. Just give them another soak and you're good to go again.