Jonathan, we had those on the snowmobile trailers, due to to be light and skinny, we mounted them all over the trailer walls.
We had 2 gallons dual packs ( 8 of them ), expensive for 32 gallons cost is 1200 ( or that is what I think we paid ).
I have seen them mounted laying on their sides 5 double packs so I guess 20 gallons
1988 110 Tdi
1987 110 2.5 N/A
2006 D3 HSE7