Tankless propane hot water heaters

If weight is really that critical that you can't manage the weight of the 6 gallons of water in the water heater, then you've probably got too much stuff in your trailer and may want to consider getting a bigger one.   I did a little poking around on the Internet and found a tankless water heater that is a direct swap for the Suburban on Amazon.  It runs about $600.  It weighs a little less than half the weight of the Suburban, thus saving you an additional 24 lbs.  [The Suburban cost almost $500.]  https://www.amazon.com/Girard-2GWHAM-Demand-Tankless-Heater/dp/B019BWN8E2/ref=sr_1_24?crid=KZEQQ40ZYQX9&keywords=tankless+water+heater+for+rv+propane&qid=1549717924&s=gateway&sprefix=tankless+water+heater+for+rv%2Caps%2C201&sr=8-24

Tankless water heaters are activated by flow, so you have to run it long enough to get the flow hot.  I'm using one right now every day for a shower and it takes quite a bit of water passing through the system before the water from the heater gets hot enough to be useful.  That amount will depend on the starting temperature of the water, the distance to the point of use, the flow rate, and the efficiency of the heat exchanger.  So, you'd want to compare how much water you will use to get usable hot water from both the tankless and tank systems. 

My suspicion, based on using one every day here in Colombia, is that you'd use pretty close to a couple of quarts to a gallon before getting useable hot water.  And if you take mariner's showers, you are going to have to reheat each time you turn the water off and on.  [The amount of reheating depends on how long it's turned off and the ambient temperature of the fresh water in the tank.]  In contrast, the tank gives you nearly instant hot water with each turning off and on, the delay being the distance from the tank to the shower and how fast the hot water in the line cools off.

Given the limited tankage, both gray and fresh, and the higher level of water use for a tankless water heater, if you boondock, such a system may not be the best option.  On the other hand, if you tend to stay in RV parks with full hookups and don’t have to worry about a limited supply of water and gray water tankage, then such a system could be ideal. 

So, the decision really depends on how you use your shower and sink, whether the extra use of water needed to get useable hot water is more efficient than lugging around an extra 65 lbs. of water and water heater for the tanked system.   I'd be interested in your experience if you change out your unit for a tankless, so please let us know.