PeeWee,
I used plasterboard that had 1" insulation pre attached. Down the centre of each board from the top, I grooved out the insulation and fitted oval type plastic conduit, then fitted a double socket into each one. The boards were then just stuck onto the wall using a cement based adhesive. So 11 boards, 11 double sockets @ 4ft pitch. Once that was done, the same board was used for the ceiling. Before fitting the ceiling, I wired up the main ring by feeding the cabling down the conduits.
I use metal plasterboard screw in plugs for holding anything to the wall, and people who have been here will attest, that I must have hundredweights hanging on the walls, with no problems at all.
Last winter I tried out one of those cheap oil filled radiators, with a thermostat fitted (less than 20 squid from Wilko's). It was left permanently on, all winter, and I coudn't really detect much change in my leccy bill, but the workshop, once the machines had absorbed some heat, had a constant, very nice working climate throughout the winter, and no condensation at all. By the looks of the weather, it will be turn on time soon.
Bogs