Spray with that Scotchguard stuff you waterproof shoes with. Seals the mold out.

without starting the Great Fire of London?

Thanks a lot, i really needed that chuckle.

Now, basically we need to dry them. We can either drown them in varnish, or burn the insides but it wont be as effective.

Easiest things is to wash/disinfect the surface before you carve, like give the pumpkin a nice bleachwater bath. Use clean tools & seal the cut edges with petrolium jelly or WD-40.

Long-term you probably could dry it as a gourd to preserve it, but it'll shrivel up a lot and look like shit.

Formaldehyde/pickling would also probably work, but i imagine it'd get all mushy.

Just this year I learnt you should carve out the top (stem) part. Apparently there's some nutrients/water, magic, or something, left in it; and if you leave it uncut it will help the rest of the pumpkin look better for longer.

Cut out the bottom, or a hole in the back, instead.

Freeze them