Just had my pipe off for a clean up while I also install some carbon tech reeds. When I put it back together is it best to use copper slip on the threads of the allen head bolts that go in to the barrel? What's the perceived wisdom of the Beta masses?

Yes, apply some anti-seize on the threads. Not grease.

ive always put copper slip on - I do on every bolt I take out to be honest

copper slip and Anti seize...great ideas/

My preference is to replace the allen bolts with studs and nuts if there is room. I see quite a few barrels damaged with crossed or stripped threads from use (misuse) of allen bolts