It is true to say that the HB payable is decided by the rent officer under the old rules however if the cost of mooring plus licence, insurance and arguably bsc do not exceed your Local Housing Allowance that all of it should be paid. LHA rates should be found on your council's website.
Unlikely you'll get much info from VOA as the rent officer is an archaic limb they've largely forgotten about. Best to claim, keep an eye on correspondence and note that you have 28 days rather than the usual month to challenge a Rent Officer determination if it is not to your liking.
The Local Reference Rent; the amount used as the maxima for the area, should be the 30th centile of the mean range rent for the area plus licence, insurance and bsc. That might still be the mean but I'll check if you ask me to once there's a decision in hand.
Feel free to inbox me if you don't like the RO's determination.
It doesn't need to be a residential mooring and as you are over 35.there is no question of the single room rate applying.