I would go with design 2... no reason to have more than one bubble trap. Here's a pic of mine before it went under the stand- it's less complicated, but sort of the same. Left- for protein skimmer, middle (after bubble trap)- refugium, right (after short partition)- for return pump.
I basically use #2 except i have a 2nd baffle between skimmer and fuge. Water travels under and over into fuge section. Then to the return with the 3 baffles