Hi Geoff
I use to have a Venture Cat 15, probably the same size as the sea-spray but with less fun factor and more ugly factor.

It is much smaller than a regular cat and also narrower.

Many cat trailer have ajustable rollers and can be easily and safely modified to fit a boat like the sea-Spray. Once you have moved the rollers that that the boat is fine, you can cut the excess tubing from the trailler's crossbars

You can also have a stock trailler modifier at a trailler shop (or do it yourself) The main things to add are:

Crossbeam with rollers and vertical guides to hold the hulls.

Front mast holder

Things to check: The tongue must be long enough the hulls need to clear the read of the car when turning sharp (especially when backing up)
The frame of the trailler should be 4'x8' instead of 4'x4' Some boat trailler base a 4'x4' base with bars that connect to the tongue fo form an A frame. There bars could hold the front crossbar but the framing needs to be heavier to keep if from flexing too much.

Wheels should be of standard size ands easy to find and replace. Also you need one spare!

Once you have all of that, you can even do some additionnal work on the trailler:
Add a sail tube
Add a trailer box
Add a rear mast holder

The best solution should be to take an existing cat trailler and simply move the rollers to the proper position

Charles Leblanc
Nacra 5.2 #28