There's probably 4 main changes I'd make to the Fuso to get it comfortable over stock.
Once you know the end weight, get the suspension designed to suit with a ride that's comfortable for you. Stock suspension is rather harsh, it's designed for full weight and a variable load, a motorhome is typically within a fairly defined range that can be customised. There's both the ATW and Earthcruiser packages, or going down the custom route. I've got the parabolics on mine, trucks not loaded yet so the ride's a bit bumpy but should settle down. Gave me 2 inches of lift over stock too.
Super singles can give you a combination of ground clearance increase and stops rocks getting stuck between the dual wheels. I've got the ATW super singles, the tyre's overkill in a number of ways (I've heard them described as a 10 ton truck tyre on a 5 ton truck) but very tough. I carry 2 spares but fully expect not to need them.
Dynamat in the cab takes out a lot of the road noise. Still to do that. Both wife and I noticed the noise bringing truck home, depending on the road conditions made talking inside a little hard at times.
More comfortable seats. Drivers side in mine wasn't too bad on the drive down, wife now won't go for more than 4 hours using the stock passenger seat, it's rubbish.