My mother's neighbor has started growing pumpkins for her to cook with. She measures it into pie portions, puts it in a ziplock bag and freezes it.
You want to bake or microwave the pumpkin -- no added water! Just scrape off, maybe run through a sieve if the flesh was grainy. Use as canned pumpkin.
Edit: The best pumpkins for cooking are not the halloween pumpkins but you can use those too. Typically a cooking pumpkin is fairly small (10 pounds or under) and with a very thick rind.
My prefered choice is Kabocha Squash, which looks like a green pumpkin from the outside!
https://en.wikipedia.org/wiki/Kabocha