AS/NZS 5601.2 : 2013...
3.4 CYLINDER COMPARTMENTS and LP GAS LOCKERS
(f) Have a drain in, or within, 25mm of the base, as per option 1 or 2 of Figure 3.4, with a minimum clear area of 500mm2 The drain outlet -
(i) shall not face the direction of travel and shall face away from any opening into the caravan, which is less than 1m away unless that opening is more than 150mm above drain outlet.
(ii) shall be at least 1.5m from any ignition source unless the ignition source is at least 500mm above the drain outlet.
Alternatively, provide vents in the compartment / locker door at both high and low levels. Each opening shall provide a minimum of 5000mm2 of free area for every cylinder enclosed and shall meet the clearances specified in Items (i) and (ii) above.
The bottom edge of the lower vent shall be within 25mm of the base.
Them's the rules above. Figure 3.4 is a drawing of a gas locker with a (vent) pipe of minimum area of 500mm2 sticking out back or out below.
Clause (ii) is interesting as I suspect there are many vans with a gas locker / storage compartment behind rear wheel (or even cylinders in boot space and contain a heater (LPG or diesel) with 1.5m.
A 500mm2 area is not very big as a 50mm x 50mm vent would give 2500mm2 , only need say 25mm x 25mm to give 625mm2. Also seems odd that drain vent only has to be 500mm2 and yet for venting locker there is need to provide vents in the compartment / locker at both high and low levels with a minimum of 5000mm2 of free area. Makes one wonder 500mm2 is a misprint?. However the above is from the Standard.