Yep, sure do. Two types that I know of. One is a gauge that screws into the neck, then your hose screws into the gauge. The other type is a thermal reactive tape that you stick to the side of the tank. Seen 'em, but have never used either, so can't say which is better or how well they work.
1) On the panel with the water and sewage tank guages. Usually in higher level models.
2) Built into the tank. More common on tanks which are fixed rather than removable.
3) Inline guages. These work on pressure, so I'm not sure how accurate/temperature dependant these are.
4) Auto switch manifolds. You probably have one of these. It has a green/red indicator to indicate whether the selected tank is empty or not empty. Also switches from the primary tank to the secondary tank when the primary is empty.
5) Tapes. These are LCD strips which tape to the tank. You pour hot water on them and read the level real quick. Never tried it and never had any interest in trying it
6) Magnets. These are LCD strips which stick to the tank by magnet. Supposedly shows the level if you get them installed right, but I never seemed to get a reliable reading with them.
I forgot to say they have a cover over them with about 10 bolts and nuts ,so I'd hate to take it off every few trips, just to check. Anything for the outside of the covers? as for above the stove I didnt see anything I looked the other day.
The thermal tape strips work quite well when you pour hot water over them, however you would still need to remove the cover over the tanks. Sounds like you have a real cumbersome system. You may be just as well off removing the covers every so often and refill the tank that shows empty on the regulator switch (RED) (see step #4 above on Hertig's post). All you have to do is switch it over to the tank with propane in it (GREEN) and remove the empty tank to fill. At that time, if you install the thermal tape strips on both tanks you can pour hot water over the remaining tank with propane in it and see how much you have left in it.
Please note that propane tanks only fill to 80% capacity to allow for expansion of the propane in hot weather. The overfill values installed inside the tanks preclude overfilling.
Probably the in-line pressure guage would be your least cumbersome option. Of course, it would only apply to the tank you are using and I don't know how accurate it would be across a range of temperatures.