DIY Diesel Tank Planning Advice

[zstine]

I have read some threads regarding DIY tanks and I just want to run my plan by the community to see if I missed something important...
I'm doing it custom because it is pyramid shaped with the top cut off and no off shelf fits well. Buying custom is cost prohibitive as I have many materials on-hand. The tank will hold about 20gal. I plan to use 11/32 exterior class rtd sheathing for my core. Stitch and glue assembly with epoxy fillets followed by 3 layers of 10oz. epoxy/glass tape on all seems, then 3 layers of 10oz epoxy/glass over both inside and outside of the ply. I plan to put GPO3 FRP piece in place of the wood core where the fittings go. This tank will be used to gravity feed my main tank, in lieu of running it as a second tank. Because it is a gravity drain feed, I want to put the fuel fitting near the bottom of the tank. A no-no for gas, but is this allowable per ABYC for Diesel? I plan to paint the outside of the tank for cosmetic reasons, but will leave the epoxy/glass uncoated on the interior as I have previously had interior coatings fail in tanks causing blockages. Any problem leaving the inside raw epoxy/glass layup? my largest panel is about 12" x 32" and will have a baffle mid span. Is 11/32" ply core, with 3 layers of 10oz epoxy/glass sufficient for strength and sealing out the Diesel for this size span? Any added comments welcome.
thanks
zach