You should put something under the Jack antenna and then use the Dicor to seal around it once it's screwed down.
Many here will jump in and say never use silicone on an RV, but many products are attached with silicone and then sealed with Dicor. The Winegard Travler antenna is a perfect example. You install it with a bead of silicone under the base and then seal with Dicor.
Side Note: I believe the Jack antenna only comes in black or white and can often stand out like a sore thumb on the roof. On my last one, I painted it to match my other roof equipment. I painted the base, not the actual wing.
Don & Mary
2019 Newmar Dutch Star 4018 - All Electric
2019 Ford Raptor Crew Cab