I would not clear coat it - moisture will find its way between coating and surface and turn hazy at best and pit surface at worst . I just polish a couple of times a year with Blue Magic and then wax . I did my own nickel plating with the Caswell system on my ES2 nearly 10 years ago and I live at the seashore- the corrosion capital of the universe and the nickel has held up fine. If you must have a coating you might want to try a product called “ Shine Seal “ . This is a ceramic coating that you simply wipe on then polish. I use it on my aluminum castings and it works very well indeed . It is pricey but it does what it claims.