Neither option is ideal but I would lean towards indoors if you have the room. Either way provide some sort of air circulation via wind or a fan or 2.

Thank you! Can you give the reason why indoors isn't ideal? Just trying to learn all the ins and outs and keep good notes for next season.

Indoors is probably fine if you provide air circulation. Ideal temperature is in the 75-85 degree range which is what you have in your house. It may take a little longer for them to fully cure. Lay them out in a single layer or hang them in bunches of 6-8. When the necks are tight and dry you can trim the roots and cut the stems down to about 1" from the bulb. If you have any necks that remain green set those aside to use first as they won't store well.

After curing and trimming I hang mine in mesh bags in the basement and keep an eye out for any rotting or sprouting.

@Robin Lawson What are you going to do with 300 onions? Just curious! I have had no luck growing anything but chives and Egyptian Walking Onions, you making a ton of Onion Rings? French Onion Soup? hmmmmmmmm

I cure mine on my covered porch for about a month with summer temperatures of 75-85°F, and then move them to my cellar for storage. Last fall I moved about 100 of my Copra onions to bins in my refrigerators. I am still eating these and only a few just began to sprout, so 11 months after harvest they are still fresh and juicy with only a few green cores. The ones I kept in the cellar slowly began sprouting in November but many remained good into February.

This year's crop shown below may be my largest onions yet as some of the Candy have already surpassed 4" with huge greens that show no sign of wanting to yellow or fall over. Probably another 3+ weeks of growing before harvest begins.