If installation pipework becomes water damaged it may leak. To help prevent this from happening the pipework must not run below bilge water level. Bilge water level can be determined by the presence of a 'tidemark', the position of the bilge pump or its inlet, or the level at which the float switch is set.
This will also protect it from other mechanical damage and allow you to smell a leak more easily if one occurs.
LPG pipework must be kept away from areas containing sources of ignition such as petrol-engine spaces and battery compartments. If, however, the pipework has no joints, and is enclosed in a gasproof conduit, it may be run through these spaces. [7.17]