Can't comment on where to fit as I did mine myself. If you're ok with home diy try it yourself it's not difficult. Took me 2 hours with no prior knowledge.
I've had a powrtouch and purple line. Both worked without issue but if I was buying again I would probably go with powrtouch as the rollers get better grip in the wet.
The best mover if you have a chassis with the "M" mark is the Al-Ko Mammut. It is completely above the bottom of the chassis so no clearance issues. The down side is about £1500 fitted
I had a fitter recommended who put me a Powertouch Evolution on. He sourced the mover and fitted at my storage place in Rotherham. He is based in Sheffield and I was delighted with the job. If you send me a direct message I will forward his number
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