Wow!!!
Thanks for all the very helpful advice guys. On reflection, it is the lugging the barrels and lifting my classic 50 litre Omnitrolley in and out that are really getting to me. Plus the extra walking back to the car for refilling etc. Waving the pole, even at height isn't too much of a problem for me - particularly since buying my SLX and superlight brush.
So..... Will look at the option of a flat baffled tank. I also have a spare pump and a good quality reel with 50 mtrs yellow 6mm hose. Might be able to make up a van mount box etc.
Filling the tank will be a doddle as I have a 300 gph immersable pump in my main storage tank plus a plastic version of the petrol station delivery nozzles.
Much food for thought - the more energy I can save the more hours I can put to earning etc.
Thanks again all - keep it coming

John