I have had several roller trailers and now a large bunk and I have to say that rollers are nice in certain conditions and if you have a good roller trailer you the boat will always seeks a dead center position. I think if you skimp on the number of rollers and don't have a trailer that is set up right you could have a problems with alignment.
I am new to bunks. IMO it is a lot easier to become off center on a bunk, but that said, I think once it is on the trailer, I think the load is spread out over move surface area with less point load pressures on the bottom. However you really need to get that baby in the water deep because you can rub the bottom hard with the carpeted bunks and I would think effectively sand down the bottom if you use it often. If you have a shallow ramp and big boat it could be a rough haul out. I am just getting use to it. I watched the previous owner launch and pull the boat (out of one of the nicest launching facilities I have ever seen) and it was painless and quick and he never touched the crank. Put it in gear and the boat slid up up the crank effortlessly, clipped it up and drove off.
Both work, bunks are cheaper and have less moving parts. I plan to put a few wide rollers along the keel just to make me feel better and ensure centering.
Van...good luck with it. IMO the worst part about trailering is the maintenance of the hubs/breaks/rotors/bearings with seawater and air...I wish someone made composite wheels and breaks for trailers that didn't corrode. I think my last trailer had 60 miles on it and the wheels froze to the breaks and I had a wash-out kit and it still corrodes.
Seawater+ air+ time+steel = nightmare.
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