Fitting of the outboard bracket was the final major task that I carried out earlier this year. I very much regretted not doing the job when the decks were off & the deck framing removed. No reason other than simple prevarication by me not wanting to cut into the sealed bouyancy compartments.

The solution largely followed an old artcile in the summer 2001 edition of Wayfarer news and an article on the Wanderer class assoc web site http://www.wanderer.org.uk/technical/outboard_bracket.htm
Plus help from this forum see other earlier postings.

As you need to be able to rely on the bracket being 100% secure I wouldn’t consider anything other than bolting solidly right through the transome and a solid backing.

In summary list of operations as follows;
Carefully mark bracket position ensuring outboard swings to avoid rudder and ensure that fixings are accessible within the rear bouyancy tank.
My bracket ended up in a position slightly different to that detailed by Boats & Bits who supplied the bracket.
The top two bolts go through the centre of the timber bearer that carries the ply deck, there was a gap of a couple of inches in which to use a spanner.
The bottom two bolts went into the bouyancy compartment, I made up a long drill with a length of 6mm ss rod and drilled right through the whole compartment. This gave me the location to cut an access hatch using a drill and hacksaw blade.
I then cut out all of the polystyrene by what ever means I could. I had thought that I could just cut out a section to access the bolts and then fix it back after but this proved impossible.
With the compartmentment completely empty I drilled the two final bolt holes. I cut and epoxied into place a 9mm plywood packing to the inner face of the transome. Then with plenty of Sikaflex I bolted through with some large ss penny washers in adition to the washers supplied with the bracket. I also changed the nuts to nyloc nuts to guarantee that they would not come undone.
The compartment was then refilled with a 3D jigsaw of polystyrene wedged into place then finally secured with expanding foam to fill all of the air gaps.
Final task was to epoxy back into position the access hatch then glassfibre over the joints to give a water tight compartment.

It all seems to work very well but be warned spending time mostly upside down with your hand in a very small tight place is not to be recommended, assistance will be needed to help hold the bracket and screws etc.

But please check & double check before drilling through the transome, my first pilot hole hit the end of a deck bearer and the whole assembly had to be repositioned.

Hopefully that all makes sense, let me known if you want any more info or details. Good luck.
Regards Peter