The single step is not as effecient as the twin step and the 312 with BBC will burn more gas......to me the additional length/size was worth it. I even pulled the head out from under the V-berth, installed a 5,000 BTU A/C system and placed a porta-potti on the floor in front of the V-berth. The compartment that toilet sat is was so small I couldn't get my azz in there anyway!!! I also made an extension for the bed so our feet were actually 2 feet out over the bench seats. Worked great, if you look through old Formula threads from 1-1.5 years ago you likely find the thread where I posted how I made all that stuff.