here's what I did for the vent line,I epoxied a brass fuel tube to the bottom of the cowl,I leave enough slack so when mounting the cowl I just slide the fuel/vent line on it.
on mine I flush mounted the brass tube with the exterior of the cowl but you could leave a little extra outside and attach some more tubing to extend it past the surface, there isn't much oil coming from the crankcase vent line but a little extra tubing directs it off the fuse.