Started by cutting the rear fender off with the razor saw:

There's a piece of plastic that needs to be trimmed where the springs go on the real thing:

This bit also needs trimming to make it possible to add the hinge pin later:

Holes need to be cut in the fender to allow the install, also the part where the hinges go needs thinning down to about 1.5mm thick:

Chopped up hinges as before:

The hull hinge area also needs to be thinned down:

Hinge glued and clamped, once set, both sides need to be adjusted carefully by bending with some fine pliers, in order to get a good fit and still be able to work properly:

The hinges in place, after adjustment. The brass wire is temporary to check the hinges are in line:

All back together, I have added a little chain to the inspection cover I made earlier and have added the drain tubes as per Philipat's suggestion.

Fenders back:

They need a fair bit of tidying up, but they do work.
If you wanted to go for a full scale look, it would probably be better to make new ones from brass sheet, as the HL plastic is quite thick, although this can be an advantage as its also quite strong.
Need to tidy these up and then on to a few final hull details