Provided it is gas tight, you should pass the BSS (my suggestion would be to make the bolt-on bit small enough to hide underneath a cylinder ):
7.2.1/R REQUIREMENT
LPG cylinders in a cylinder locker:
Cylinder lockers have many advantages as a place to stow LPG, but
they must meet certain criteria to comply with the navigation
authorities’ requirements and national and international standards.
LPG is one of ‘the most searching gases’ and will escape quickly
from any weak point.
Is the cylinder locker LPG-tight up to the level of the top of the
cylinder valves or other high-pressure components?
Check the extent of the LPG-tight area of all LPG cylinder lockers.
Check the condition of all cylinder locker and housing bottoms and sides.
Cylinder lockers must be LPG-tight to the level of the top of the cylinder
valves, and other high-pressure components where these are located
higher than the valves.
Within the required LPG-tight area, the bottom, sides, and seams of
every cylinder locker must be free of holes, cracks, damaged welds,
significant corrosion, or other damage.
The above requirements also apply where any part of cylinder housing
forms a part of the craft’s hull or superstructure.