Hi Keith
Yes, it is a topic I have always been interested in. Many years ago, a friend and I found some genuine WW2 Jeep canvas tops , stored in the back room of Hudson stores in Bourke St., in the city. The tops were moth eaten and torn here and there. We used them for a while on our Jeeps !
Yes, the 'real' industrial sewing machines are expensive, over $1000 or more. Many people sell machines that are actually only semi-industrial, basically these are only heavy duty domestic models . These are OK for many jobs , Jeep tops and such , even seat covers which are relatively light. But for the heavy weighted canvas as used on Blitz and other vehicles, you would definately need a stronger machine with a 'walking foot'. The walking foot feature , pulls the job through , which you need with multi layered haevy canvas . Most of the domestic and semi - industrial models use a simple presser foot which just presses the work onto the serrated dog beneath.
In the factories, the machines were set up to do a certain job 16 hours a day . It's not a straight forward thing , as there are many variations of feet and such for leather work etc. Believe it or not , there are clones of the 1950's industrial Singers being made in China today, they tend to be of dubious quality though. Singer designs were copied by many companies.
A machine like this would be ideal :
http://www.industrialsewmachine.com/...inger/211a.htm
Mike