Hello from Denver!

Two comments on your mods (podmods around here).  With option 1 of the battery upgrade (parallel), it is important to connect the pod's negative to one battery and the positive to the other, to balance the charge and discharging.

As for the propane gauge, as mentioned already they don't work due to how the propane tank works.  You end up measuring the pressure created by the evaporation from the surface area, which will be uniform until you get to the bottom shoulder of the tank when the surface area will slightly reduce.  But that happens at the very end and often when you aren't looking and by then you are just about too late.  I do have an easy solution for you that does work and doesn't involve removing the tank - the hot water method.  Pour a cup of hot water slowly down the side of the tank from the top shoulder, wait 10 seconds and then run the back of your finger down the side.  Where it is hot you are above the liquid level since the heat is retained by the steel, below that it will feel cold since the liquid absorbs the heat.  Because of that it won't work if the tank is sitting in direct sun.