Hello and thanks for the info & links
Yes should have posted some background info first...
OK based on our caravanning history: we only use CL's / CS's (CC and C&CC) and tend to avoid those with HU's. There's just the two of us (+ 2 mutts) and have always managed with a single 100AH battery using the 40W panel. The last two caravans were all LED lighting, we've never had a TV (and no intention of having one), so the only 12v power used was for water pump, lighting & radio/CD player. Fridge / hot water / heating / etc was all run on propane.
We bought the 40W panel and solar charge regulator in 2003 (!?! I didn't realise it was that long ago!) after lengthy discussions with a 12v solar expert. It's always charged the battery back up after an evening's lighting + music then 2 x showers, breakfast & washing pots in the morning within an hour or so... The 40W panel is on an Alu frame I made that we can alter to match the suns angle in the sky and move to follow the sun's track, so never a problem getting enough charge from March through to October (our typical "season"). I see that you can now get calculators online at the solarelectricityhandbook website.
So - a 100W panel mounted horizontally may be needed to make up for not being able to track the angle / position of the sun; plus the low cost of the latest panels and solar charge regulators (ie MPPT) is a revelation when I consider we paid £250+ (after *much* shopping around!) for our set up 11-odd years ago!
Will go away and count my shekels, and do some more thinking...