Sam,

i love your projects; So inspiring!

Regarding the pumpkins, you will likely have noticed that these squash plants will re-root into the ground along the length of the vine. This is probably what allowed it to grow so long at the car park. This may have limited the growth on the pumpkin house.

Regarding alternatives, i would recommend a simple pole bean. Plant one side and then plant the other side 2 weeks later so that all the beans don't come at the same time. i used an heirloom called Kentucky Wonder but there are many.

Here is a photo of the beans we planted in Mexico. i planted them very close together, every 2". They ended up climbing 10 feet and created a lot of shade.