I have a Jaz 15 gallon fuel cell that I want to stand on it's side, instead of lying flat as it is now. This is to make more roo in the tiny trunk of my 3 window coupe I'm building.
I've looked at buying or building a tank that will fit, but this idea that popped into my head seems like an easy and economical way to achieve what I want.

Right now It has the D ring filler cap, a pick up tube and a vent on the the top what will become the side. What's the best way to plug these holes up?

Nuts & Bolts with washers should handle the two smaller holes and I was thinking of making a block-off plate where the big filler hole is now and permantly sealing it.

Questions are:

What type of sealing washers will work with gasoline?

What kind of sealant will work on plastic and is impervious to gasoline?

Any ideas?