Where the guide poles really help is a windy day. They're sort of like goal posts - go slow and get "somewhere in the middle", and it "catches" you. Yes, you can add the bunks while the boat is still on the trailer. Snug them up tight to the hull. Then, when the boat is off, slide them in an inch or so and you should be good. But, you need to check that there is a suitable mounting spot for them and that the mounting spot can handle sharing the load of the boat. This doesn't work out on all trailers.