I believe Seth is doing an apprenticeship and plans on returning in the future.
There are others who do a lot of Bougies,
@JoeH ?
@SU2 ? I'm drawing a blank as to who else.
In general, there are two approaches to thickening trunks. Let grow long and tall without pruning, often done with pines, and many deciduous. When trying to bulk up the diameter of a trunk in a tree or shrub or vine that must be kept in a pot, there is the logistic problem of getting the pot into a protected area for winter. Letting it grow unpruned for the bulk of the growing season, then chop low enough and bring in the branches enough to be able to easily move the container in autumn, before bringing into the greenhouse or garage is the normal routine.
What thickens trunks is the total surface area of leaves the trunk supports at any given moment. Tall and leafy or wide with many branches with leaves is equally good if the total leaf surface area is roughly equal. So let grow tall, or force lots of branches with leaves, both approaches work quite well.
Key is keep lots of leaves. Then the trunk will thicken.