2018 Tacoma Header Rail Gap Seal Issues

I have been having the worst time trying to weather proof my Leer topper due to the header rail gaps where the side rail meets the header rail. So far I have removed the header rail, put butyl tape underneath it, and filled the gaps with butyl tape. This did stop a lot of water from getting in, but has not completely stopped it from creeping in. After some heavy research on the topic I have found a couple of threads about people filling the gap with Part# 1118059 REV A. I think this foam comes in a kit, but I was wondering if anyone knows where to find this part. Below is the foam ends that match the part number. If anyone has a better idea of non invasive ways to fill the gap (not great stuff or other products that cannot be removed) i'm open to ideas. Thanks!

 

Maybe

https://m.lowes.com/pd/Dow-GREAT-STUFF-Multipurpose-Black-12-oz-Spray-Foam-Insulation/1000172523

 

@Rujack that's exactly what I don't want to do. This should fix the leak, but this product is not long lasting nor removable. If no elegant solution presents itself I can resort to this, but I'm trying to go with a better solution. Thanks.

 

Retrax has those pads with their kits. You could see on getting some or making your own.

A bead of silicone is what a lot of shops do when they install shells. That should be removable if needed in the future since not sticking to anything porous.