That's not just poshcrafters that do that, ex squadies are the masters in that area
There was this one time in the Squadron bar.....pull up a sandbag you'll like this......these 2 mec's from a REME LAD are taking a stollie for repair when.........
We've owned our caravan for about 4 years and in that time we've never used the caravan shower, preferring to use the on site showers.
The problem with caravan showers is that you've got to clean and dry them once you've finished and they are bound to promote damp which is the killer of any caravan.
I know quite a few Travellers and they never use the on-board facilities in their Caravans
Not only that, but we've only done a 'number two' in it a very few times, again preferring to use the site loos. The obvious reason for this is that if you put it in, you've got to get it out, and that's not a pleasant operation.
The French have their system of Aires de Service and these are geared up for Motorhomes. You can drop Grey water, Black water and also refill the on-board water tank(s). Some Aires are known as Aires Stationment and those are the ones where you can stop over-night-safety in numbers but I usually wild camp EG on our Motorhome we can carry 200L of fresh water and 230L of grey water. We also have a bulk black water tank that can hold some 45L of grimness; emptying that can be hilarious. I have seen some Boxhead catch the lot on his van when the solenoid valve stuck
There are hardcore Caravanners who use their toilets and showers for what they are intended but I think you're right that there aren't many.
This seems to be mainly a UK thing according to a couple of dealers that I know quite well