Max Towing Capacity of tow vehicle?
Max Tongue Weight of tow vehicle?
Weight of Trailer?
Tongue weight of trailer (loaded)?
Weight of Boat (Consider weight of gear, fuel, and possibly water)?
Other things to consider is distance, amount and grade of hills. The big concerns are really: Can it perform a controlled stop in a reasonable distance? Can it haul the boat back up the ramp?
I would want some room for safety. I would be hesitant if the total package were 7.5K and I had an 8K max. for example. I know that fuel, water, gear is going to be underestimated in my equation somewhere.