My mucker Bertie has just had a gas tank fitted to his bus.
Price included a tank full of gas.
He had it done in Gloucester, I know that's not very near Merseyside
but it's the only one I know.
They took 2 days, but allowed Bertie to stay in the bus on their
premises overnight with hook up, and supplied a courtesy car for use
during the day.
If you want further details, contact Alan (Bertie) Bassett through
his posts on this forum.