Probably sounds right to me also. We use our camper year round, until the outside temperatures reach about 10F above zero or less. In the Summer months we may go 2 months on 1 thirty pound tank. We run the water heater on gas too. In the winter, using the furnace, we can run through a 30 pound tank in 3 days. When the usage gets that steep, we move back into the house.
There is no set pattern for anyone's usage of propane except your own. Time of year makes a big difference with outside temperatures, even for water heaters and cooking on stove tops. In addition, the amount of water you use, the more hot water you use will require the water heater to run more too. If go from one shower a week to a shower every day, there will be a big difference if hot water usage. If you do 2 showers a day, it will be even more usage. You can only monitor your own usage and track it that way.
If you had a propane leak, I think your tank would empty itself MUCH faster than 24 days and you'd smell it somewhere.
The soap test is a good idea, just to ease your own concerns, and doesn't hurt anything, except, maybe the soap will wash down your pipes (which isn't a bad thing at all).
I think your usage is perfectly normal. Track it, see if it's consistent. If you start having to fill up a tank every other day.... then yes... you've got a problem if you've been consistent with a 24 day usage cycle.
Good luck!