I woul look at the bunk style or the post guides then invest in the ones you think will solve your problem. I'm getting ready to switch my 21' boat from a bunk trailer with post guides to a roller trailer and I know I will need the guides to center the front of my boat on the rollers. I could center the boat with the bow line then drive on the trailer or winch it up. but its just easier and faster to just drive up and let the guides center the boat then drive on up.

I use a 4000# electric winch on my trailer for the times I cant power load. and it will pull the boat right up to the bow roller. and that's on my bunk trailer. I just back in where my bunks are about half covered then start the boat on the trailer and hook up the electric winch and winch it up. if the guide ons doesn't solve your problem you might want to think about going to a electric winch. just get one big enough to winch the boat all the way on the trailer. the winch I plan on putting on my roller trailer is the superwinch lt 4000 lb off ebay for 179.99.

good luck on the guide ons.