Trailex and Kitty Hawk are the best two options. The gunnel supports are at the strongest points of the hull/deck and will never crack. Just make sure the boat is well secured to the trailer. The trailex has softer springs, (I've owned both and put a lot of miles on each) but the kitty hawk is more solid/sturdy.
There are spar holders designed for the deck. I got a great set through APS. If you want to double stack there are racks available that allow you to put one laser right on top, (deck down) of the first and hold all the spars between them. I would do this with the kitty hawk, but not sure the aluminum frame of the Trailex would support all the weight as well.
Yes, that can be done. Put it on upside down and secure it. Since it comes apart so easily (Seitech dolly) I just break the dolly down and put it in my vehicle.With the Trailex and kitty hawk trailers, do you just strap down your beach dolly on top of the hull?