I bought a 2013 19' Bankes Crusader last spring that didn't have trailer guide-ons. My 20' salmon boat had the PVC uprights, that got the boat centered, but were troublesome at times getting the launching ropes over the tall upright posts.
I went with 2' side bunks from Wholesale Marine. Because my custom built trailer has 1/2' "play" getting the bottom channel inside the bottom bunks, I knew any side winds at all with these flat bottom boats would be a headache to get the boat on right the first time.
Well, these side bunks work great! 6 trailer loadings so far and it has been a perfect 6 for 6. No pulling the boat out to see it's not seated on the bunks right,
backing back in to float it over, etc, etc, etc. You know the drill.
And I've seen the uprights get bent out when power loading and having winds blow you into them when driving on the trailer. Like Jim and Phil, I like the side bunks.
Steve