Propane...

Watch the RED/GREEN indicator.......
When Green turns to RED then 'in service cylinder' is now empty (that would be the one lever is pointing to) and auto swap reg has changed over to other cylinder

Flip lever to other cylinder.....RED goes GREEN

Remove empty cylinder and go get it filled.

Repeat when Green goes RED...cylinder is empty...swap get MT one filled

How large are the tanks? I have dual 30 lb tanks and never had to fill one after the first season. I'd suggest just opening one tank then let it run out completely that way you know you have a full reserve. The easiest and most reliable way to determine the level in the tanks are to lift them...you can tell by the weight when you are getting close to empty. Don't buy those stick-on gauges, they are junk.

When we had a huge propane tank for the house, we would go out and throw a bucket of hot water over it, then run hands down the side of the tank. The empty top part of the tank was warm, the part with the liquid propane in it was cold. Primitive, but it worked.

Tiger4x4RV wrote:
When we had a huge propane tank for the house, we would go out and throw a bucket of hot water over it, then run hands down the side of the tank. The empty top part of the tank was warm, the part with the liquid propane in it was cold. Primitive, but it worked.

They make temperature color-changing stickers to apply to the tank that work similar, a little more visual, but still pretty primitive.

I do how Iraqvet05 suggests, I leave one tank closed, when first one runs out, I know I still have a full reserve and manually open the 2nd one, and then I have plenty of time to go get the other one filled.

Leave both open , watch the red 'green , tanks will last a long time , When gauge turns red you are then running on a fresh tank . Look at gauge every 2 or 3 days . Only a real dummy will run out !

My tanks don't have indicators....you can tell be lifting one up or when the flame goes out. Mine last through a whole season of camping. I just changed out a tank from last year that I used, when it was empty. I even used it some to run my heater during the winter when I was out there working on the inside of the trailer. I don't know what size your trailer is though...mine is a 25RS. One thing to check is if your tanks are older they have a date stamp on them for re inspection.

You might try one of these.

I bought 3 - 20 lbs tanks at Costco...and they came with some sort of majik gauge.....

I have one of the auto changeover regulators and the plastic cover. Since I leave the heat on in the winter I needed an easy way to check the fuel.

I cut a 3" hole with a hole saw over the gauge and now I can glance at the gauge any time I am walking past.

the problem is that propane in the tanks is a liquid, it evapourates in the tank as you are using it. so the pressure in the tank doesn't change as the propane is being used until its empty and too late

a mechanical level guage is the only reliable way, similar to a gas guage in your vehicle

the ones at Costco are the only rv sized tanks ive seen that have them and no, I don't use them. when a tank runs dry, switch over and fill up