I doubt that it's 27 feet long - the F18 mast is something like 29'6". For a temporary support, go to West Marine (or Walmart near the coast) and buy one of those square 'throwable' pads and put it between the mast and the rear beam. The Nacra rear beam has an integrated traveler track and you don't want to put wood or anything that could damage that track on top of it. Pad it well with the cusion and tie/bunji the mast and cushion securely in place.

Rollers on the trailer is probably OK for that boat because it has skegs. The bottom rear of the boat is well reinforced with the skeg. The front could probably use cradles but as long as the rollers are near bulkheads you should be fine for a while.