Advice/links re cargo bike conversion

bikedoc2

New Member
Hello
I wonder if anyone can advise me re my cargo set up .
I am a mobile bike mechanic and frequently use an xtracycle conversion to carry my tools and some spares. I also tow a Surly Bill trailer to bring bikes back to the workshop .
This is all fine for flat journeys or for up to 3 or 4 miles but I should like to be able to travel 10 to 20 miles each way without nearly dying .
Does anyone feel able to advise me re motor type, voltage, wheel hub motor or via bottom bracket/chain wheel please??