At the moment our brakes and suspension get serviced by Vehicle Components in Brisy as part of the warranty but after that I will be doing it all, I did it to our campertrailer and this is really no different, just a little bigger. I usually go around and check everything before and after every trip or at 12 months. When we bought our van I went around and did a, I suppose you could call it a "pre-failure maintainence program" and checked what needed to be replaced or fixed to "my satisfaction" and there were a few things on that list too.....

The water tanks should be cleaned out every 12 months, I leave them full in between trips though, and depending on the time between trips, either I will drain and refill with fresh water or leave the water in there. Every 12 months I clean the tanks out with a little bleach (you can use milton as well), I use about 50mm of pool chlorine per 100-150L of tanks, drain the tanks a little and using a funnel tip the chlorine in, top up with fresh water, go for a drive to slosh it around, let it sit for a day then drain the water out (I also run a bit through the pumps and pipes to help clean them out too), fill it back up and slosh it around again, drain it out, re-fill with fresh water, this you may have to do a couple more of times depending on how much chlorine you have used, I flush ours about 3 or 4 times to get rid of the taste, but I think I may have used a little too much chlorine this time around. I only ever use proper food grade water hose for filling the water tanks on the van and I use an inline water filter from supercheap (explore). Never use a standard garden hose to fill the tank, the water will be tainted by a plastic taste and it can be very hard to get rid of it.