Propane locker for 11 lb. propane tank

For safe transport of a propane tank on board, boats use a propane locker, which is an airtight container holding the propane tank, with a vent in the bottom so that any propane that leaks from the tank will drain out the vent. Propane is heavier than air, so it would sink to the bottom of the container. There are safety specs from the American Boat & Yacht Council that call for an airtight container that opens from the top, with a bottom vent at least 3/4" inner diameter.

I made a propane locker for my 2019 4Runner to hold an 11 lb. Worthington propane tank. When installed inside the vehicle, in the rear driver's side corner of the 4Runner cargo area, I can still access the OEM jack and tire changing tools in the quarterpanel.

The propane locker is made from 3/4" plywood. The 11 lb. propane tank is about 9.1" diameter and almost 16 7/8" high. The overall exterior dimensions of the propane locker are 11" x 11" footprint, and 18 1/2" high (plus the handle screwed to the top of the locker). After gluing the box together with wood glue, I painted the inside and outside of all seams (where two pieces of plywood meet) with 2 or 3 coats of epoxy resin, to make sure the seams are airtight. For structural strength, I reinforced the inside corners of the propane locker with trunk corner brackets.

To secure the propane locker in place, I screwed the inside of the propane locker bottom to the plywood floor that I had installed in the cargo area, and also braced the bottom of the locker using a couple DIY brackets made from 1/8" angle iron screwed to the floor. To prevent the propane locker from tipping forward in a sudden stop, I installed a crossbar holding back the front-facing side of the propane locker. That crossbar is bolted to a shelf system along both sides of the cargo area that I installed to provide interior storage space.

The top of the propane locker has a gasket cut from 1/8" thick natural rubber sheet. Actually, because of inaccuracies when I glued the plywood pieces together, I had to use two gaskets: 1/8" and 1/16" thick, to ensure a tight seal. The top is held down to the main body of the propane locker with 7 latches.

The vent at the bottom of the propane locker is an assembly of stainless steel plumbing fittings that go through an OEM hole in the sheet metal floor of the 4Runner. The underside of that hole is open to the air, so any leaked propane that passes through the bottom of the propane locker, through the plumbing fittings, will dissipate harmlessly outside the vehicle. An elbow fitting just below the 4Runner floor directs any leaked propane rearward; the opening of the elbow fitting is covered with stainless steel mesh (secured in place by a stainless steel hose clamp) to keep mice out.

I took this propane locker with the filled 11 lb. propane tank on a 3000 mile trip, and it worked out well. No damage to the tank, no leaked propane, no rattling of the tank against the inside of the propane locker.

 

Interesting, looks like this pretty much solves all the issues mentioned in the other thread regarding permanently mounting a propane tank inside the cabin of the 4Runner.

 

nice design. one thing i'd worry about. have you tested to ensure that when you are driving that the airflow from the bottom vent is going out in all conditions? also, tested all configurations of Heat/AC and various windows being open in differing amounts?

 

i haven't tested airflow through the vent. But when in use, the propane locker has no openings to the interior of the vehicle. It is completely sealed (if the gaskets are doing their job) except for the vent at the bottom, which opens to the outside of the vehicle. So I'm not sure how open windows or the ambient temperature inside the vehicle would affect airflow through the bottom vent.

If there is propane leaking from the tank, it will first go into the inside of the locker, so the pressure inside the locker will become greater than outside, and the propane will be forced out the vent to underneath the vehicle.

Some additional pictures of the interior of the propane locker and the cargo space underneath the locker:



The inside of the lid of the propane locker is shown below. I couldn't make a simple 6-sided box because the interior wall of the 4Runner is curved at the rear corner of the cargo area. So I had to make a 2-tier box; fortunately, the top of the propane tank is smaller in diameter than the main body of the tank.


The photo below shows the top view of the open propane locker when standing behind the rear bumper, with the rear hatch open. The circle drawn on the bottom of the locker shows where the bottom ring of the propane tank sits. The vent through the 4Runner floor is just left of center. I cut a hexagonal hole in the plywood bottom of the locker so that it fits around the hexagonal fitting. Then I used 100% silicone seal to fill the gap between the fitting and the edges of the hexagonal hole. If this gap is properly filled, then any leaked propane will not leak under the plywood bottom of the locker, which is still inside the vehicle; instead, it will pass through the hole in the center of the fitting, to outside the vehicle. For safety, it is critical that this seal work properly.


The space underneath the locker (before installing it) is shown below. The wheel well is in the top 1/3 of the photo, the OEM jack is on the left, and the edge of the plywood floor that I installed in the cargo area is on the right. The top surface of that plywood floor is higher than the 4Runner sheet metal floor, so I put a couple wood spacers over the sheet metal in the corner. The propane locker rests partially on these two spacers, and partially on the plywood floor.


SAFETY ALERT. There is one major disadvantage of using a propane locker like this. Apparently, propane tanks can explode once they reach 120 degrees F. On a hot summer day, with the windows closed, the temperature inside the vehicle can get much hotter than 120 degrees. So the propane tank should not be transported inside a propane locker like this on hot days, unless the temperature inside the vehicle can be kept well below 120 degrees at all times. However, this propane locker could be used in winter, Spring, or Fall, if the temperature inside the vehicle is always well below 120 degrees.