Well... possible - but you would have to be running 3 approx 1000W devices on different branch circuits before you trip a 30A main...
Much more likely to trip out the individual 15 and 20 amp breakers by plugging 2 devices into same branch circuit - even if on 50A pedestal.
Should have mentioned though - I would run the water heater on propane - or at least switch it over if you have an issue - as that makes it much more likely to trip out the main with other loads.
Not yet retired...
Florida (Michigan transplant)
2014 Hurricane 32A
2000 Infinity (previous)