I'd be interested if you can recall which vertical tank you used.
Kevin
650 x 250mm 64 litre Stako from WTV. That holds approx 51 litres of lpg, which enabled me to travel from Bristol to Penrith. It's a * very* tight fit but will go in if you persevere with it. I pre-assembled the convoluted vent pipes to exit the body behind the bumper and was able to pull them into place with a stiff piece of wire.
The tank was secured to a hidden length of angle iron which I bolted to the body reinforcing web just above the rear wheel arch. You can use the redundant spare wheel retaining strap to prevent the tank rattling, but it must be securely fastened to the vehicle body by a strong steel strap or bar for safety and to comply with installation regs.
If you're not too bothered about range then the smaller 630 x 225mm 53 litre is a simpler installation. That holds approx 42 litres of lpg.

650mm is max possible diameter.
I glued some offcuts from rubber floor mats in place above and below the tank to stop it rattling against the bodywork.

And you won't squeeze in anything fatter than 250mm either


The spare wheel cover can be held in place with a bit of velcro glued to the tank

A small gap between the wheel cover and boot edge is all that gives away the tank's presence.

I've got some more pics from OMVL Dream XX1n installations on saloon and estate Omega stored on another computer which I'll post if I can find them anytime soon...
Regards,
Martyn H