Re: proper towing questions
I honestly wouldn't bother weighing it... I know iboats likes to go a little crazy on towing, but seriously... Its an 18 foot glass boat, and the vehicle is rated for 5k. If that boat is over 5k, you have FAR more serious issues to worry about, like trying to figure out how to pick the frame off the pavement, because the trailer is going to be laying flat on it.
The OP didn't list year/model, but there are current model 18 foot glastrons that are under 2k WITH the engine. Older ones with a 2 stroke could even get you down to the 1500# range. 3500# is a high estimate but safe estimate of the total weight down the road. 5k is insane.