Hi Tris,
I grow my Tomatoes outdoors here in Ireland and it is indeed a gamble. You wont get a crop as good as that grown in a tunnel or greenhouse. But I think it is still worth the effort.
I would make two observations on your wigwam.
Tomatoes need to be planted 2 – 3′ apart for good air circulation. You don’t want a humid environment around the base of the plants as this creates the ideal environment for blight and other diseases. Airflow is also improved if you remove all the leaves below the first truss.
As for support, you will need something more robust than a bamboo. The wind plays havoc with these plants especially when laden with fruit.
I have a frame from which I tie strings down to each plant. As the plants grow I twist them around the string. The same system employed in greenhouses/tunnels.
Don.