Not in a motorhome but did travel around Australia with a tent.It was an excellent idea and I loved every bit of it.I have met a lot of couples in their fifties and they all had positive experiences.Most people stay in interesting spots for up to 2 months and then move on.The advantage of a motor home is that you can stop at a lot of free or very cheap national parks.Basically,you plan out a basic route of which way you want to go and what you want definetly see.You meet a lot travelers on your way and usually they recommend places where they have been that are good and they also tell you places that you should avoid.I found that this was an excellent way of getting the information as travel brouchures would often paint a completely different picture.
We mostly camped in proper camping spots because they were well equiped with hot showers and camp kitchens.I would recommend you join a camping chain like BIG4 or Top Tourist,both of these give discounts on your camping. However,I found that BIG4 parks were much better equiped and the quality of the things they offer is also much better.
Also,we spent a lot of money on going on different tours and for entries into places.I am not sure how much money you are willing to spend on these things but these kind of things can swallow up your money quickly.Therefore,it might be a good idea to agree on the things you want to visit in advance and stick to it.Believe me there are hundreds of things that will come up during your trip that you have not planned for.
The other thing is food.We did not use a lot of take away and restaurants.This means that we only had about one cooked meal per day usually at dinner time and a lot of BBQ's.At each stop we did our shopping and then only needed to buy bread and basic things from the camping store.
I would also reccommend a good GPS system and a CB radio and a mobile with good coverage(if there is such a thing)