You are thinking like a fisherman skipper thinks where they drive onto the trailer and their forward motion on rollers literally lifts the boat onto the half submerged trailer. With bunks and heavy boats you are risking all sorts of bad things. 6K 7K 10K is common for a small trawler and will fold your trailer in half if allowed, so I go slow pulling the boat along with lines. Once the bow is aligned and hooked, the stern is still floating two to three feet above the submerged trailer. The direction of the floating boat is downward not forward when pulled up the ramp. This means the guides must be parallel to the hull, at the widest point and at least as tall as the distance the boat is when floating above the bunks. On my NT 26 I have a small, heavily reinforced bunk on each side very near the winch stand. Those bunks center the bow only. On each side at the hulls widest point, I have a 2" water pipe bent to match the hullcurve and the chine. The galv pipe is attached to the six inch trailer frame with heavy clamps that slip (no damage) when the boat hits too hard. The pipe is topped with a three foot padded carpet that extends to the gunnel when the boat is floating. I marked the carpet for proper depth after trial and error. I have done this system on several large transportable boats including 33 foot sailboats with 6 foot draft. RE: Custom trailers. I have owned and used both double and triple axle rigs and much prefer two heavy 8K axles over three lighter axles. The greasing system is another stickler for me but I will let that go for now.