Good Morning! This method works well. Weigh your tow vehicle ready for the trip (full of gas, all people and items in place) at a local truck stop (Love's, Flying J). Hook up the trailer as it will be taken on the trip and then weigh both vehicles as if they are a semi unit. The scales are set up with segmented platforms. You will have two weights. Subtract the trailer weight from the tow vehicle and you will have your tongue weight. It is a little intimidating at first to get in with the big boys but once you do it you will be set and can get your tongue weight anytime you want.
Dennis