When you say exhaust vent, I presume the one on the the sidewall of the coach and not the manifold coming off the heat exchanger. Clean the surfaces and use a silicone caulk. It can handle that heat with no problem.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7