Here's mine specifically moulded for an ST5.4 :
Avon Searider - Bow locker Construction
Will refine the moulds slightly this winter and be making a few to order, first one will be grey and is already promised to go to a good home.
Post is 65mm stainless anchored into the hull with an extended u bolt and very large spreader plate stainless mounting round the upper fibrglass moulding and located on a quick release pin inside. Top of post has a welded bi-colour nav light.