Professor Fingers here (remember him?) with some numbers:
- 30lbs of propane has 378,000 BTU at the generally accepted figure of 12,600 BTU/pound
- Assuming you want to raise the water temp approx 80F (from 60 to 140 - Atwoods have a 140 degree thermostat, Suburbans 130), 378,000 BTU will heat 4725 pounds of water (1 BTU raises one pound of water one degree F)
- 4275 pounds of water is 569 gallons (8.3 pounds per gallon of water)
- which is 95 complete fillups of the typical 6 gallon water heater.
the typical RV water heater is probably less than 50% efficient and then there's standby losses so make that 47 or less complete fillups.
Only you can judge how long it takes you to use that much hot water according to your usage.
That's why those of us that have a WH that has an electric element prefer to use it if the electric is included with the campsite fee.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam