I use a 25l fuel can in the bow area in my SR4 to get the trim right. Just a thought, why not put a hatch in and make a locker just big enough for a fuel can. Then you have ballast in the bow and an emergency reserve of 12 or 25 litres of fuel.
Rib Tigga an Avon SR4 Rescue with Honda BF50
MMSI 235910073 Callsign T123046