Check out https://www.youtube.com/watch?v=Mn0m104NVAY for how I tied and tightened all the knots.

If I did use holes though, assuming I kept the lincoln log joints as well, then I reckon that would weaken the joints too much, e.g. crack the pipe on hard impacts. Also all the weight of all the bolts would add up quick. Hmm I suppose I could use plastic bolts of some kind, but then they'd have to be thicker, thus making the holes bigger, thus weakening structure further. Just thinking out loud. There could be a way, but yea I was proving the lashing concept first and foremost.

Thanks for the question. :)