Mike,
Multi-use is definitely where it's at. Geoff got me started down the rhumb line with his diesel tank below the cabin deck. I think there'ld be no way the keep the smell in check. 338 has it's gas engine hanging outside. Sweet water for voyaging in a ballast mode seems like a good idea anyway. At one time I thought of putting the batteries down there, but you 'perts would have dressed me down for that. Right?
Deodorized kerosene could be stowed there. How would a cruiser otherwise carry the fuel - in gallon cans? I hadn't got the dip stick made yet when the inspectors arrived to shoot the boat. Planned to fill the tank a gallon at a time and mark the stick accordingly. Check for leaks this way. Of course I thought about an official 'fill' but forgot to put it in. So have to do that and it's easier to proof if the lid is accessable from both sides.
Have looked into kerosene for cruising, we've talked about it on the forum. The belly tank would be a way to carry fuel for stove, heaters and backup lighting. But the smell issue rears its ugly head. Don't know. I committed the tank to Sc80 PVC fittings, not brass like Geoff did. Is PVC ok with fuel oil?
Found a site where a couple of Slovanians are looking for venture capital to swing a diesel ob into the market that doesn't weigh much more than the four stroke. And it would burn biofuel as well. Bet they looking at the middle of the market, be a long time befor a ten horse would drop below 250#!!
I got some nice bronze access plates on sale. (Mariner's Hardware) Wanted 6" but went for the 5 inchers.
5 means that I can't really get my arms in the hole (especially in the shallow end). Sometimes I feel like a motherless child.
From the multi-use stand point - it would be a great place to keep cured olives in brine Or wine.