I would love to have a go at building a tm but in reality to get it right it takes a hell of a lot of time.
our unit is near the Guy who is restoring Bluebird he has enginering company and knows his nuts and bolts, asked him to look at a prowler and said he could do a better job of it . So said great! how much? worked out a grand and a half more. English quailty English Price!
So orderd another one from restormate instead. saved a few bob and loads of time no doubt as well
However do intend to just keep the ones we have running with spares from now on, as we will have a spare one to change over if one fails.
I think mikes right though a simple cheap engine suplies all the power you need. we had a 13hp one running 250ft of 2inch hose and a 25ft 1.5 inch whip and cleaned a stately home no probs. 500 square meters in 8 hours and 90percent of it dry when finished. just last room left damp
There was a power cut in the hole area untill lunch time so would have been up the creak without a tm.