I went into a local trailer supplies shop and bought a plastic mudguard to fit a 15" wheel. I bolted it to the little ali. guard at the front end, and made a bracket from side to side screwed into the wooden frame at the rear, with just one small bolt to hold the guard. A little fiddly, but not difficult.
I have a theory that Morgan do not fit a guard as they like to encourage owners to bond with the little fellow early on. It's a bit like clearing up the poo that a new puppy leaves on your lounge carpet. When it starts chewing the furniture and curtains, it is certainly a test of loyalty, just like needing new engines, exhaust bevels and compensators is.
In fact, I think we have more reason to refer to the little chap as a puppy than anyone.
Does yours have a name? [Other than 'Morgan' of course.]