Not certain I understand your question, Mario, since the whole point of getting a Tom's hull is to replace the poorly done Trumpeter hull. Fitting the poorly done Trumpeter lower hull to the new Tom's upper then totally defeats the purpose...you are essentially putting back what you sought to correct/replace in the first place. So, the question seems odd.

If you meant using the Trumpeter lower hull on the Tamiya upper, it is still an odd question. The Trumpeter Hornet kit's hull--upper and lower--are "notoriously" horribly shaped. Far too blunt, and the lower hull is missing the bulbous forefoot. It is considered so badly done that Tom's released an entirely new upper hull to correct it.

So...no...you "can't" (don't really want to) use the Trumpeter lower hull for anything... (If you see what I mean.) It is the object you are trying to avoid with all this aftermarket stuff in the first place. Additionally, since the Tamiya kit is under scale, the Trumpeter lower hull will not fit the Tamiya kit; it will be too large.