My 22L tank's gauge window decided to part company with the tank recently. As the gauge is about as much use as a chocolate teapot at the best of times, I am thinking of replacing the tank (and any subsequent failures of the 30L tanks) with a gauge-less one.
not necessarily, more the packaging space that;s important - for example I can sit 2 x Hulk 30L tanks side by side between my A- frame braces. The 22L tucks in under the seat like I suspect the way it was designed for the 5 gallon metal tanks that were the norm 25 years ago.
Idelaly like to keep some of it portable for refuelling trips without the aid of the trailer!
We do a 24 liter one, but have not got one here at the moment so I cant give you the dimensions just yet. 22 quid though.
We supply a fair few 42 liter tanks as a removable tank (no quay side petrol here), any bigger and it becomes a bit of a job. They measure 50x35x30cm. £65.
Hole is 32 square! 
