Flare fittings are very common on many boats , and a tool for creating flairs is at NAPA for just a few dollars.
If the tool is to be used for much on board work, a flare fitting tool from the refrigeration trade ($35.00 instead of $5.00) is well worth the added expense.
Although plastic like Pex is sometimes used on boat water systems , considering the time just sitting , I prefer 5/8 copper tubing.
Copper Tubing also makes long a life fuel system with no dissolving from bio fuels , today or tomorrow.
TO Flare properly is an easy skill to develop.
IF you purchase pre made rubber hose for any job , be sure to request swivel fittings at BOTH ends.