With regard to inside seams, my kayak has very acute angles in places towards the stern, and I scratched my head a little before I tried this method, and it worked perfectly.
I took a long enough strip of wood to get into the end, put a small nail just through it with the point angled towards the end, caught the cloth tape on the nail, held it lightly but taut against the strip, and then pressed it onto epoxy I had already painted along the join. Aligning it was easy, and the strip could be used to press it into the angle, after which I wet it out thoroughly with a brush on a stick.

I contemplated sheerclamps, but this was much easier. Also I did the seam in thirds with small overlaps, the middle third being all that I could reach by hand inside the cockpit. By the time it coame to the other inside seam I did the whole seam start to finish in 20 minutes.

Even easier than it sounds.

Hope this helps.