Several of us R-25 owners have had Loadmaster of Port Clinton, Ohio build trailers. That might be a little closer for you in Maine. I've generally been happy with mine. It was set up to carry the boat on the first try without adjustment. It is structurally sound and the frame and bunks extend far enough back to allow you to use the rear tie-downs on the boat. Other manufacturers require the rear tie-down to be a long strap over the cockpit. Loadmaster should have the plans on file.
Suggested options include; galvanized steel frame, stainless steel hardware, electric-over-hydraulic brakes, LED lighting, a wiring pigtail to connect to the wiring harness in the anchor locker, stronger aluminum wheels and 15-inch load range E tires, two spare tires/wheels, stainless steel disc brakes and something other than the standard plastic license plate bracket. Some people carry a spare tire mounted on a spare bearing/hub.
You'll get varying opinions on the need for rear guide bars to align the boat onto the trailer. I wasn't sure whether I needed them, so I had mounting brackets welded on so that they could be installed later if necessary. After eight years, I have done fine without them. Some of this may be due to the Loadmaster forward bunk design that centers the hull easily when loading. After contacting the forward bunks, I use the rudder to center the bow as I drive the boat up to the bow roller. Using this technique, the stern always comes out within an inch or two of center. Driving around the launch ramp with a firm stop will center the stern completely and drive the boat forward the last few inches to the bow roller. The disadvantage to the Loadmaster forward bunk design is that it will swipe of a little of the bottom paint each time the boat is loaded or unloaded. You should also be aware that if you drive with guide bars installed, you'll exceed the 8 foot 6 inch width of the boat.
Other manufacturers have done fine with aluminum frames, although trailers manufactured by Float On have a serious problem with fender cracking.
It's important to use a realistic weight when specifying a trailer. My boat weighs 7000 lbs empty even though the brochure stated 5740 pounds originally. I have neither a generator nor air conditioning, so some boats are much heavier. I have weighed the boat on the trailer at about 9500 pounds including a quarter tank of fuel and some cruising gear. I suggest that you specify at least 10 percent higher than that and shoot for around 800-900 pounds of tongue weight. The original trailers sold by the factory were inadequate for the realistic weights, although that has since improved.
Now if only I could get a sales commission?
Rich