Hunty
The recommend sealant should be Mastic. When I installed my snorkel - that was what I was advised by the manufacturer. Also use Zinc based paint to stop the rust as a primer but can be used as the final paint and over that if you wish with the colour of the jeep itself if the zinc shows..
I understand the nerves - I had the same problem
BTW
WD40 is a good lube to use when cutting