Thanks for asking me this question.
I'll start with a few basic suggestions for you to try first. If none of these, or any combination of these don't help, please ask me again and I will ask you for some further information that might pinpoint the problem.

1. You didn't state in your question what amount of water you used in your mix. (You absolutely correct in mixing the seasoning in water first, and then adding to the pork.) The most standard (but not absolute) water to meat ratio is 2 lbs of water for every 10 lbs. of meat. If you are using this 20% water to meat ratio, you could go up to a 25% water to meat ratio.

2. Don't overcook the kielbasa, as this tends to dry them out. Check the internal temperature of the sausage with a good meat thermometer (I like the digital ones the best). Cook to an internal temperature of 150 to 155 degrees max.

3. Lastly, if there is anyway to add moisture to your smoker while cooking, do it. Most commercial smokehouses have 100% humidity inside the smokehouse when they cook/smoke kielbasa. If you have a water smoker, you're probably already adding moisture to the air. If you have a "plain" charcoal or gas bar-b-q grill, you could try taking a clean tin can (like from a can of corn or green bean), strip off the label, and fill it three-fourths full of water. Set it on the charcoal or briquettes upright and start the fire (or gas). The steam generated from this will help add moisture to the kielbasa.

Try these first. I suggest try the #1 tip first. If this works, great. If not, try #1 and #2 together. Hopefully, 1, 2 or all 3 of these ideas should produce a more moist sausage. If not, please ask me again. I'll be happy to try and find an answer for this problem for you.