Re: rollers or bunks for aluminum
On any boat, rollers should be positioned to load the boat, making it easier. If the boat shape allows it, bunks should be used to support it.
The reason is, when you're going down the road, it has bumps in it. When the trailer bounces, most of the resistance to the motion is the weight of the boat. Rollers have small contact surface with the boat, and the momentary pressure of the bounce can be high enough to do damage to the boat. I've both owned and seen other aluminum and fiberglass boats that were damaged by rollers.
My trailer, for a 150 hp bass boat, has keel rollers to help pull it on if it has to be dry loaded. The last foot going forward the boat rises up onto bunks. Lashed down, one keel roller is touching, the others are 1/4 inch from the boat. Setup is 20 years old, and no bottom damage to the boat.
I had an aluminum flat bottom boat (16' Quachita) once that I bought real cheap. It was beaten to a pulp. When I looked at it, I found that all the damage was from trailer rollers.
I fixed the boat, and built up a bunk only trailer for it. Used it for years, and sold the boat for more than I paid for it.
hope it helps
John