It would have been simpler asking how to cook an egg. Whatever it is you do, it will be a learning experience so keep good notes. Just grab the bull by the horns and hope for a soft landing.
Your lightbulb may well work. When I have draft issues due to smoke temps being the same or lower than the ambient temp, I use a simple aquarium air pump to push air past the tray type smoke generator. It provides just enough air to keep the smoke moving through the 22cf. product chamber.
Did a test for you on my 22 cf. cold smoke product cabinet. It is a converted, well insulated, soda cooler with an florescent light along the door.
Ambient temp 73° product cabinet temp 69° - florescent light off
Ambient temp 74° product cabinet temp 84° - florescent light on
The temp difference with the light on would be enough to create air flow.
Hope this helps.
The AMNPS can be temperamental if it doesn't have sufficient air flow, it gets too cold or the pellets are cold or wet. Some pellets just seem to burn more reliably than others. I am not sure what altitude you are at but many on here have reported difficulty keeping it alight at higher altitudes. The reliability of the burn depends on several factors and whilst some do not seem to have a problem with reliability others do.
The mailbox orientation is not ideal for keeping it alight under non-ideal conditions as it burns for some of the time with the air flow and at other times against it. I used to have a problem with burn reliability until i rotated the AMNPS through 90 degrees so that it was never burning against the air flow. This means that the burn is always heating the new pellets in front of it helping to keep them dry.
Augmenting the air flow also helps both keep the generator alight and also to keep a good flow of smoke through the chamber. Rather than pump air in through the smoke generator I prefer to suck it out through the flue. When pumping air in you can have the effect of fanning the burn in the generator which makes it burn faster and hotter and produce more smoke. By sucking the air through the flue the flow of air is maintained - but at a more gentle rate. The easiest way to increase the flow is by using a small computer cooling fan. If you can get one that is variable speed then that is ideal. You don't even need to permanently fix it to the smoker as it can be held in place with something like bluTack while you are cold smoking. One I use for this purpose is the SilverStone
I do not have a photo of it connected to a UDS but here is one of it temporarily in place on a Weber Kettle.
This isn't using a mailbox but you may find this useful for tips on preparing the pellets for a smoke.
Yes - Which problem are we going to narrow down first, It seems that there are a couple of separate but related issues here...
I think that we need to look at both the air flow through the smoker and the generator itself
Dave will help you out with the MB. I use an retired wood stove for my firebox. From the pics it looks like a little elevation of your smoker might help as well. Perhaps setting it on cinder blocks would be enough.
Dave has you going on the MB. Now raise the smoker so there is more of an incline. You are getting there.