OK - I'm cautiously optimistic about the revised setup I made today. Pondering the factory diagram, and those of the several generations of Volvos I have owned, I surmised that my main mistakes were:
1) running the 1/4 vent hose below tank level
2) separating the 1/4 and 5/8 circuits.
So, in my continued effort to NOT put the vent tank back, I revised the 1/4" vent line to connect with the 5/8 line. This way, if any quantity of liquid either makes its way up into the line, it will drain back into the filler neck connection, as it would with the factory setup. The 1/4 vent then continues in a loop, and goes back out to connect to the factory line up to the canister. The underside of the canister was still damp with fuel from the prior setup, however after I wrapped up & drove around for a bit, went to Home Depot, left it sit, came home, the canister was emptied of fuel condensate (bottom of canister felt dry to the touch). I'll check it again tomorrow before I reinstall all the hatch trim.
Tank end, elevated the vent hose
elbow coming out of cabin
Tool for installing these fittings, makes it much easier
4 way connector is from a Volvo tank vent setup