Your old cylinder may be worth a little re price of copper.
So you can knock that off the price.
I'm not sure if I posted, build a tray to go under it.
Simple plywood with preservative & battens around the edge on
silicone; or with fibreglass flashed over it. You just want enough to
retain water sufficiently to give "indication of a leak" rather than
it being hidden. If a floor goes you can get into floor, joists, bath/
sink/shower out, ceilings & walls out if built on the floor,
decoration and retiling, which gets into messier refurb issues re BR
where tradesmen & insurers get involved.