We have a gravity feed for water for a camp. It's a 300 gal water tank about 30' above the camp. It seems to be enough to trigger the propane hot water heater intermittently but not consistently. If we increase the pipe size from the water tank, will it be enough to trigger the hot water heater consistently (it's a Morey low pressure hot water heater). There's no electricity at the camp. There is a generator but we're trying to avoid using it for hot water.

Increasing pipe size will not increase pressure. Volume yes, but not pressure. If the tank is 30 feet above the house, then you will have around 12 or 13 pounds of pressure.

I looked around a little and came up empty, but I'd try and see if I could find a gas powered booster pump of some sort to get your pressure up. Either that, or an electric pump to use with your generator for short periods to take showers.

I am going to try to show you a simple test first- This won't cost you anything to try!

1)restriction on output side of water heater could cause an issue.
If you have a valve on the exit side of the water heater close to it-hopefully a few feet- just open it and let it free flow. See if this will consistently trigger the start of the water heater. The reason I am having you do this first, is because the restriction on the output of the water heater can be as much a problem as the pipe coming into the water heater. It may be even that the cabins closest to the water heater will trigger it and those further away might not, or might not all of the time. If you can open the valve and get the water heater to turn on every time, it suggests that the lines going away from it are too small and restricting the amount of water that gets through the heater. Hopefully this won't be the case. (unless you are starving the water heater and that brings up the next scenario)

2)Too much water usage elsewhere in the system is robbing the water supply to the heater.
There is a possibility that something else may be running at the same time and starving the water heater of water. If this is the case then a larger pipe to the camp or water heater should help.

If this is going to be a major expense I would do some testing first. If it is going to be easy and a low budget item, then a larger pipe from the tank to the water heater certainly won't hurt anything and may give just enough extra to trigger the water heater and provide some buffer in case of other issues. That being said, flow(which is gallons per minute or whatever unit you use)is what triggers the heater. More pressure will give you more flow, but putting in a larger pipe will not give you more pressure, but more flow at close to the same pressure.

If I confused you let me know and we will take it one step at a time. I gave you a lot to swallow in one gulp. Kindly get back to us. There are some really good pump guys on this site and one of us will get you headed the right direction. Your input is all we have to base our recommendations on, so we like to cover the basics first if we can.

There is a possibility that something else may be running at the same time and starving the water heater of water. If this is the case then a larger pipe to the camp or water heater should help.

That is true. You would certainly know if that is the case. I am assuming it is not, since you did not mention it. I'm not familiar with the propane hotwater heaters. However, 12# of pressure is pretty lame and I don't think you will be satisfied with it, so I would look for some sort of solution long-term.

At the present time you have a little over 13 pounds of pressure. If you Google "Battery operated water pumps" you will come up with a selection that you can use to increase pressure, This must be installed like a well installation with a check valve on the tank and a bladder tank to maintain pressure. I know of only one more way to increase your pressure and that would be to elevate the water tank. For each foot of elevation you will gain a little under a half pound of pressure. Can you raise the tank? Let me know. In my estimation your best option would be the pump that runs off a 12 volt car battery. Back to you, Tom