Best sealant for side of fifth wheel

So we picked up our brand new fifth wheel last month, and though I don't think my wife is happy about it I already plan on poking holes in it :)

I am going to mount a cell booster antenna on the side and so I need to poke a hole through the side of the rig to run the antenna wire through.

The question though is what is the best sealant that I should use on the side of the 5th wheel to seal up that hole I just created.

Thanks for your time.