I've got a choice, I need to put a layer of hardboard over the floor because the boards are dead rough and to match existing levels where the boards have been covered with hardboard. I can install the suite on the floorboards and then cut the hardboard to fit around the WC / pedestal or install the hardboard and put the suite on that. Anyone got any thoughts on whether I'm likely to have problems putting the suite on hardboard?
Wouldn't use hardboard, if it gets wet it disintergrates, I would go with a cement fibre board like a 6mm backer board or similar, what flooring you putting down. A backer board is waterproof and dimensionally stable unlike hardboard.
In any case, fit the sheets first and then sit the pottery on top. Don't cut the sheets around. Ditto with the vinyl floor - you'd be nuts to try and cut and shape that around the pan and pedestal.