I have found 20' Procraft Boat, its older but has all been restord and has a rebuilt engine. The question I have for you is, it only has a single axle trailer and weighs around 1700lbs..Do you think it will make much of a difference from a tandam for towing???

If it wasnt safe, they definitly wouldnt have put it on a single axle. Just be sure to carry a spare hub, tire, and the tools needed to change both of those. Its also paramount to keep up on the bearing grease packing.