CharlesC,
I have done this a few times on the roof when necessary and no issues.
It would be sensible to minimise the weight were possible by removing spars and foils, but two boats worth of kit should be fine.
Be sure to get adequate padding in the five positions shown. If you have one of the white 'delivery' cocoon covers they have pads fitted.
Tips;
- Remove the mainsheet ratchet block (on both old and new types). Laying it flat and padding it is not sufficiently low.
- Make sure all the fittings around the mast step are inserted into in the mast step and not proud.
- Tie boats firmly at bow and amidships so they can not move