The two sketches below are ornamental gourds but are not bottle gourds. The first uses senbyō-hō only.
This next sketch is the same except gansai (colored ink) has been added. This outline approach with color filling the inside is another example of the kōrokutensai-hō approach.
Here is my demonstration painting, chosen as my way of celebrating Thanksgiving. The still life has a bottle gourd accompanied by a sake (酒) cup, implying that that is what the gourd is filled with. Happy holiday!