I've read a number of articles on this. One method said to use 1/2" PT
plywood 10" wide triangular shims every 24 inches to prevent water from
getting between the beams, and to let it dry out by the PT Plywood.

This seems odd to me since this would tend to weaken the beam? Does
anyone really do this? ALso I would thin kPT Plywood would be a lot
less durable than 2x10 PT? Is it really practical?


Also, let's say my header is 12' long. What carriage bolt spacing
should I use? I was thinking 24", staggered on-on-top, one-on-bottom?

Thanks!
BX1