I found out the hard way about setting up rollers/skids
The trailer actually needs to have the weight of the boat distributed evenly on all the rollers for the reason that boat trailers are designed to use the weight of the boat to stop flexing. Enough flex over time will cause stress points on the trailer and eventually cause it to fall apart.
My first trailer had skids fitted and I found them difficult when winching up the boat or even launching. So I asked a lot of people about how to set them up, eventually I listened to some people that had boats and trailers for 30+ years. Their advice was to setup the skids to that they only just supported the weight of the boat. I found this to work great, the boat came on and slid off with ease.
Unfortunately these people with 30+ years experience never went on any long trips. My first trip within 3 weeks of owning my new boat/trailer combo was 3000kms one way and it was on my return trip I found out out about trailer flex
The new trailer I had built is fitted with rollers, rollers, no skids and more rollers. I ended up consulting a structural engineer about setting out the rollers. What we ended up with in the end was enough of the boat weight on each roller so that you cant turn them by hand.
This is currently working very well and the new trailer has about 8000ks on it.