Thanks guys. I'm packing to sell my house so I haven't had time to video any demos, but I'll try to do some soon. This is also that time of year for me that, like Nat_ster, I have a million "things I do to make money" all starting at once.
Originally Posted by Rayzer69
I am wondering if it would be possible to make a fiberglass understorage box 12' 3" long x 30" deep x 30" high. one section would hold a 40 gal/320lb fresh water tank and one section would hold a 400lb battery bank?
You can definitely do this, but for something that long you may want to think about whether it's cost-effective (and worthwhile) to have the box itself support those items. You can make structural shapes like channels and beams just like you can get with steel - and they do exactly the same thing. The Cozy's front-seat floor pan is just 2-BID (each side) over 1" PVC foam and supports two adults side by side. I'd double the fiberglass to provide some extra crush resistance, but this isn't that hard to set up.
But... batteries need to be serviced so you're going to want to be able to slide them out. That means some type of tray or drawer, which you could mount to the bottom of the bus with a simple frame of bolted angle-iron. You can do the same thing with the water tank, and that doesn't really even need to be serviced so you can just support it with steel straps up to framing members.
Then if you still want a box you can do it just to provide a sealed environment for the above. But now it doesn't need to be structural - it's just a simple shell. That means you can use very thin (cheap) foam and only 2 plies of fiberglass. That would give you a sealed-environment box for much less cost and work (and worry?) than wondering if you got the structure right on your first "go".
If you want to do the structural work with fiberglass (for fun or ...?) I have a different kind of fiberglass that's confusingly called "tape" even though it bears little resemblance to the thin stuff you use to bond two panels together.
I'll post a photo of this later today - the one here in this link sucks, but it's this stuff:
UNIDIRECTIONAL FIBERGLASS TAPE from Aircraft Spruce
This stuff is incredibly thick - I think it's like 1/8" thick (which is very thick for fiberglass) and it's strong as hell. The Cozy main wing spars contain "I" beams made of this stuff. You don't need much - a single layer can be used to make a "strap" that has the same strength as a steel one. A pair of straps made of this will easily support a 400lb water tank.
One drawback to this stuff is you can bend steel, but not this. You need about 1" radius on any corners it has to go over. But... it'll never rust...