You might want to try this before installing guides. After you have launched, if you want to spray the bunks that is fine but not required. Load your boat as normal, just don't winch the boat forward, but DO attach the bow strap. When on level ground, not on the angled ramp. Tap your brakes---lightly! The boat will slide forward up to the front roller. Then you can winch the strap tight. It is easier on the strap and on you. No real difference on the hull as you normaly are winching the weight up anyways. If done correctly, the boat stays centered since the rear bunks have done this for you. If that makes sense. Works on boats from 17 to 23ft that I have experienced.
Nothing wrong with guides as long as they do not vibrate going down the road causing rub rash due to being mounted to close to the hull.