I haven't tried lox, but I did it with boars. I'll assume the same.

Use a saddle to get one on - might need to build a bit of a ramp like above.

Harpoon won't work at all, unless you turn pvp damage on.

And like someone said, avoid enemies at all costs cos they will get over the boat side.

I'd suggest only using the paddle. The boats jump too much if they go any faster and the lox has a far greater chance of clipping through and/or damaging the boat.

And set off at the start of day, preferably a sunny one. Night and rain increase chances of serpents, as well as waves.