IMHO, trade between these entities would be limited to a few items.
1) Raw materials needed for whatever industries exist in both areas.
2) Very high end consumer good heading to KFS.
Reasoning:
KFS and Texas both need raw materials as they continue to grow the military and the economy of both areas.
Texas, esp 1st Cav would not want to deal with the repressive KFS. But greed is still greed. Any high end consumer goods would be targeted toward the Rich Five and the higher ranking administrators.
Once KFS launches the conquest of surrounding areas, I think that Texas would cut all trade.
Depending on time line, IF Texas problem with Mexico is at low simmer, I could see 1st Cav deploy toward KFS. Not to attack, but to defend Texas. IF 1st Cav is rebuilding after latest attack from Mexico, KFS could take huge chunks of Texas. In this type of scenario, Texas is in DEEP do-do.
My two cents worth!
Mike