Back when I was in university I couldn't afford a snowmobile trailer. I put a 4x8 plywood deck on my 16' boat trailer to haul my snowmobile. It worked, but not well. It was a pain to take the bunks off the trailer to set up the deck, and again in the spring to put them on and line them up so the boat would drive on properly. The boat trailer didn't tilt, so I always had to carry a ramp. The trailer sat a little lower in the front and without reverse it was tough to get my sled off the trailer alone. As far as weight distribution goes, you won't need to worry about having enough tongue weight! Usually the motor is the heaviest part of a small boat and hangs at the back of the trailer. A snowmobile is the opposite, most of your weight will be ahead of the axle. Mine tracked behind my old s10 like a lawn dart!
If you drive a full size truck it's easier to load it in the bed, or if you can save up for a month or two, watch kijiji and marketplace for a used tilt trailer for a few hundred bucks. It saves a lot of headaches!
