not sure what the vehicle looks like
When the concern is for gas, that is not a good excuse in my books. First, go slower and you will get better gas mileage and if not experienced and no brakes, do not go over 45.
Not sure if the boat is on a KWS or Kens welding trailer. Does it have surge brakes and if so do they work. This is most important. With surge brakes working, should you brake, the trailer will brake and you can feel it. Without brakes is a very careful situation. Let me explain.
If you are going fast and the trailer starts to wobble on you, the tendacy is to brake. You could loose the boat and car because it will cause the trailer to sway much worse to the point you could have an accident. What you have to do is accelerate and then brake slowly. This is only if you do not have brakes or brakes that are not working. I am considered the expert on this.
If the trailer is a kens or kws, then check the bearings and racers(greased) and attachement of fenders. Make sure you have 10% of the load on the trailer tongue hitch and tires are full with air.
Your vehicle is able to tow up to 3600 pounds. you are appx 3100 pounds total with boat,trailer, motor and junk or more if carrying allot of gear. If carrying allot of gear, put it foward in the boat.