Okay, I made the mistake of reading about the tapeworms during dinner. The description of the "Basenji burrito" was quite amusing though…
I agree that it's going to take some time, but just because he has separation anxiety now, two weeks after going through some pretty MAJOR life changes to be with you, doesn't mean he's going to be just as anxious two months from now. If you're seeing improvement of even minutes within days, just imagine what you'll see even further down the road.
After a HUGE international and cross-continental move, my Shiba had some pretty bad separation anxiety. He wasn't destructive, but he was howling, and since we lived right next door to the landlord, this was a problem that we had to nip in the bud...
We trained him by repeatedly leaving the house and coming back, going through these drills for thirty minutes to two hours a day. Starting small, exiting the door for 30 seconds (giving a verbal cue), then coming right back. Then building up to a minute, two, five, etc.
We figured we had the problem resolved when we were able to leave the house for an hour. We'd give a verbal cue that we were leaving, let him hear us go down the steps outside the apartment, and then quietly sit down on the stairwell and read/do whatever. That way, we were within earshot in case he started howling, so we'd know.
One thing we made sure to do was not to return while he was howling. As far as I could tell, it wasn't continuous. It'd come in bursts, going for a couple minutes at a time, pause, then a couple more minutes. I do have to admit that there was one time early on when he started howling and did NOT seem inclined to stop. What I did then was I lurked outside the door while my partner tromped down the stairwell... when he started howling, I quickly threw open the door, startling him, told him NO (he was sitting right there), and quickly closed the door again. It actually worked! He remained quiet for five whole minutes after that... Now, I'm not sure if that was because I gave away that I was just outside the door. But this correction really did make the rest of our exercises much easier, and I didn't have to "surprise" him like that again.
After we settled into a routine, things became easier as well. For us, it WAS an issue of our dog being uncertain not just about our absence but also his new environment, so it might be similar to Sebastian's case. If your goal is to help him become more self-sufficient, a regimen like this might work. Maybe you could crate or pen him in one room while you do something in another room for a while, instead of going in/out of the house.
...
Another thing I've recently been using, for another issue (OCD licking of paws, but also related to anxiety) is anti-anxiety drops. Many rescuers sing the praises of Rescue Remedy. Ingredients: impatiens, star of bethlehem, cherry plum, rock rose, clematis. I'm using a similar product with different ingredients, Homeopet Anxiety drops. Ingredients: Chamomilia, Valeriana, Borax (which I understand is alarming to see on a list of ingredients, but it's supposed to be okay here?), Cypripedium Pub., Ignatia A., Colch. Verat. A. Both seem kind of pricey for the tiny little vial that you get ($10-$15 for 10 to 20 mL), but since you're only supposed to be using drops at a time, it goes a long way. You mentioned that your budget for over-the-counter medications is limited, but I just wanted to give you some options.