You have a couple of problems I think. The first is that the tube smoker creates way too much smoke to cold smoke in such a small chamber. Even in my 650 Litre cold smoker the tube produces smoke that is too intense. Something like an AMNPS will produce smoke that is less dense over a longer period of time. The second issue is that you almost certainly do not have sufficient air flow through the smoker. I am not sure which of the Rec Tecs models that you have but being a pellet grill they are will not have a lot of natural air draw - relying on the integral fan to manage the air flow. The combination of both of these will result in very high moisture within the chamber and the risk of a creosote-like condensate forming on the meat.
What Dave suggests is certainly worth a try too. By cooling the smoke before it enters the chamber much of the tarry condensate will have condensed out before it comes in contact with the food.The temperatures can be quite difficult to control practically though over long smokes (24 hours +) as the outside air temperature will vary greatly over a 24 hour period - especially at this time of year.
You could try emptying out the pellet hopper(s) and place the smoke generator in there (rather than directly in the chamber), but without an extractor fan on the flue to pull the smoke through you may not get the smoke to flow through the unit. You may also gum up the pellet feed auger.
I would second Dave's suggestion regarding using a cardboard box. Holes in the bottom and holes in the top to let the heat of the burning pellets natural create a natural air flow through the unit.