No offense, sounds like you bit off more than you can chew. Sounds like you need a better set of instructions, check you-tube and see if there are any videos on how to do this.
Mount the dish where indicated by the Vegas roof plan, that will be the strongest area and the dish doesn't care if it's on the centerline or not. You can run the wiring from the dish in the same place as your antenna. For sealer you can use the 3M 5200.
Sorry but I can't provide any more help than that. Best of luck with your install.
Dave & Myra
One day your life will flash before your eyes,
make sure it's worth watching!