Putting keel rollers on it would make it very difficult to load the boat Tony. As it is with swinging cradles it is virtually self centreing, if you add keel rollers you will loose that I think and have to centre the boat very precisely for recovery. I would prefer the self centreing ability especially with the wind and current I launch into.
What I would do is increase the number of rollers on the cradles, if there are only 4 to a cradle you could double them up to 8 by adding another couple of bars. if there is no room then you could contact the manufacturer of the trailer and get the next size cradle they make, the parts are quite often interchangeable. If there is room you may also want to consider adding another complete swinging arm with another set of cradles / rollers as far back as you can.
Also give them a good dosing with Wurth spray grease or simiar, it goes on thin but when the solvent evaporates it is real stick and slippy. Mine is sat on 40 rollers and is a one handed launch but I do keep them all well greased.
What I was considering was keeping the cradles, and the first keel roller would come into play after she has climbed over the rear cradle.
One just behind the axle, one on the axle, then one or two in front of the axle.
The trailer would still be the same two swinging cradles but if I get it right, about 60% of the boats weight on the keel rollers, well thats the theory anyway, I was going to make crossmembers from wood in the experimenting stages, and when I get it right, fabricate steel box section to match the trailer, that would be clamped in place. Then once I'm satisfied, get it galvanised before fitting.
Or does that, not sound like a plan?
At the moment when she comes over the rear cradle the boat also tends to go nose down before getting on to the forward cradle.
Rgds Tony