Gasoline fumes hang around from 0-18" any clear area in that range is acceptable. Try to get into as clear an area as you can so you can move as much air as possible.
The hose which goes to the blower should end as low as possible in the bilge. Secure it with plastic straps to keep it from moving. That's the suction hose. The other hose, the feed, should be at about 2' off the bottom of the bilge. That feeds fresh air. Hy