Are you sure it's IBS? I'm wondering if what's ailing Freddie might be EPI?
There are (at least) a couple of EPI support groups on Facebook who could guide you to proper testing/diagnosis. And there are a few basenjis in the group: EPI - Exocrine Pancreatic Insufficiency in Dogs (Original). Another group is: EPI - K9EPIGlobal.
Best wishes to you and Freddie in getting this resolved.
@ashmoore92 I don't have cats, but I would do some training, enrichment, walking or playing with the pup to expend some energy before letting him interact with the cats. And, I'd have him dragging a 4 foot leash. Is this your cats' first up close and personal experience with a dog?
Here's an article I came across recently. Hope it helps...
I don't know where you live, but unless your garage is climate controlled it might be too cold in the winter and too hot in the summer. Would it be possible to confine your pup to the kitchen? He certainly doesn't need the run of the house. That's what I've done for my dogs for years in two different homes and it's worked out very well. In my current home the kitchen flows right into the living room. I have an ex-pen across the opening, using a couple crates (I have 2 basenjis) and the loveseat on either side to keep the "fence" sturdy. But you can get gates of all lengths and configurations at most of the pet supply places. I also have beds in the kitchen for my dogs and access to one crate, but neither one will use it. I wish knew how to post a photo so you could see my set up.
I think you're doing all that you can. I let my boy go as long as possible, in addition to the CCD he was having seizures. He made it just over 15. He had a good appetite up until his last day. I knew he wasn't going to get better, so I made The Hard Decision.
Once my basenjis demonstrated that they no longer tolerated being crated I expanded their area by confining them to the kitchen/breakfast room using baby gates. It worked beautifully and still does. I rarely need to be gone more than a couple hours anymore, but I always walk the pups before I need to leave.