If cooling is your main concern then a motor conversion with coils wound in slots on an external stator has the best cooling, you have fairly direct heat transfer to the teeth and then via the core to the outside world.
For wind application slotted iron cores have some issues that to me at least are more important than cooling. The main one is iron loss drag in low winds, others seem more concerned by cog.
I like the idea of a slotless design with coils in the air gap, this can be built in various ways and the method shown has considerable merit for wind use. The magnets can't fly out of the drum and the large drum makes a very good backing to the blades and it retains the nice bearing arrangement of the axial machines, conventional bearings with shafts as in motor conversions need hubs to mount the blades.
It is much easier to wind coils for a stator with no teeth and fix them on the outside of an iron ring, I have built them with coils on the inside and a magnet rotor on the inside but it is far more tricky.
The cooling is not as good as with the stator on the outside but it is still much better than the air gap axial machine as you have direct contact from the coils to the iron core and then to the core mounting back plate.
If you want the best cooling with this type of construction then it would be better to build it with outer stator and projecting magnets on an inner magnet rotor and put up with all the other associated problems of attaching magnets and having to use a hub.
My own view on the various forms of construction is that the simplest method for home construction is the air gap axial. Those with a fear of windings seem to go for motor conversions but mainly these are people with mechanical skills and experience and have machining facilities.
These are the ones who would also have the skill to build a slotless machine as long as they were prepared to tackle the winding side of the construction.
I think the reason why Hugh went away from the drum design was that it was too mechanically complex for basic home construction anywhere, especially the finding of suitable components without machining is a real challenge.
We see a lot of excellent mechanical work here and this form of construction would be an alternative approach to the axial for many people but for first time construction I still advise copying a proven design. Hugh's ferrite magnet design is a bit dated and I haven't seen any published details of a drum design that first timers could copy. Even if I could find the details of my drum alternators I don't have time to do the detailed drawings suitable for beginners and most of my machines were not built for direct loading direct to the battery, they use converters so the windings are different.
For those with a bit of experience and machining facilities the radial slotless drum alternator is well worth looking at and I am very surprised that we haven't seen more of it here. If you can't do the calculations for emf then test coils as for the axials would be a sensible starting point. My advice for anyone trying would be to keep the coils no more than 1/4" thick, if you go much more the winding becomes tricky and the heat transfer to the core becomes far less effective.
Flux
