The proof of the pudding is in the eating, or in this case the proof of the mods was in the beef. After modifying the Brinkmann to give me easier charcoal access, air control in the base and somewhere for the ash to fall I think it was a success.
Cooked a 1.5kg joint of beef at the weekend in it, 4 1/2 hours and managed to keep the temperature at a higher more consistent level than previously, being able to lift the top off to get to the charcoal means you can turn the charcoal to lose the ash, topping up is a piece of cake. As far as the air vents are concerned it possible now to actually affect the temperature of the unit, although only in a hotter/colder way, open for hotter, closed for colder. The only problem is that the ash generated although falling through the mesh I installed is filling the void, next time I will need to make sure I remove the ash when topping up the charcoal.
All in all though a great success! Just got to try the cold smoking now, I have the soldering iron (40W) although I won't hold my breath that it will last too well, its a homebase special.