Companion Planting; Pumpkins and Watermelons

I'm still debating adding a few peppers to the bean rows in Greenhouse #1, but I'll wait and see how many extra pepper seedlings I have to deal with first.  For now, I've added radish, onion and corn to the Pumpkin patch, and Nasturtium, Sunflowers, radish and peas to the Watermelon row.

I moved the Romaine to the front and back edges of the greenhouse, not because it serves any particular benefit to the pumpkins and watermelons, but because it can be finicky in my northern garden, so I want some in the greenhouse.

Now I am debating in my head- if I plan for Greenhouse #4- what would I plant in it?