Mine are simular to the ones in the link. Bit taller though. I drag my boat on, never had any problem. I have drove it on once with no problem. I back the trailor in until the rear corner of the guild is touching the water.
Guide ons make loading the boat a breeze. Always loads centered. Mine were actually included with the trailer, there are many diff types out there.
just google trailer guide ons..
I have short upright roller guides located near the back of the trailer. You can see the port side one just above the license plate in the below foto. Even with them I had a hard time centering my boat when loading. I installed some self centering bunk guide ons and have yet to fail to center on the first attempt since then. I have loaded my boat on the trailer at least 8 times since I installed them.