See post 7 above.
Page 13 of the STC installation manual has the instructions and diagrams.
Fuel slap is hardly noticeable on my van, just hear a gentle sloshing after the engine has been switched off. All depends upon degree of carpeting/insulation as to what is heard.
I reckon that you are picking up the noise through your ducting - you could try some Thermoduct to insulate it and cut down noise transmission.
