The length of run of the vent hose is irrelevant so long as it is not obstructed and it makes a vertical loop close to the thru-hull to prevent water accumulation. If your fuel fill is slow, it is likely an obstruction caused by insects--wasps are famous for that. Moving the vent to the side of the boat risks the possibility of water intrusion when one is well heeled.
As for your chemical smell, it may simply be uncured/poorly cured resin. One thing that will help is using activated charcoal to absorb the odors. You can obtain activated charcoal at an Aquarium store fairly inexpensively. Eighteen inch lengths of ladies nylon stockings with knots on each end make convenient containers (fill them shore-side as there will be a cloud of charcoal dust when you do so). Drape these around the hoses and they will absorb the odors very quickly. I have used the foregoing to handle the invariable odors from a holding tank under the foot of a berth in our quarter cabin and the offensive odors are all but gone so long as I replace the charcoal annually.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."