the truth is 100m hose is a nightmare in the winter months if your using a cold water set up,at least install an immersion for softer hoses if you cant afford/cant justify spending a few grand on a diesel heater.....
the coldest weather is usually between dec-march.....thats a long 4 months with cold water,also if you install an immersion you can be sure you wont wake up to a frozen system,its a miserable start to your day.......and more chance of you sacking the day off and suffering from low motivation in general.....
as for cheap gas shower heaters...from personal experience i wouldnt recommend them to anyone these days.....IMO its not worth the risk plus they are unreliable and break easily and its a faff changing gas bottles all the time...
if you ve just bought a new/nearly new van and plan to keep it for a long time and are earning well out of your cleaning business then i wouldnt hesitate to recommend a professionally installed diesel heater from grippatank or pure freedom...they really are a joy to use......