Hi packardbell,
We are British and we had a two week holiday in a camper (a small motor home) here several years ago. We toured Scotland and northern England.
You might be following a pre-planned route or just pottering around ending up wherever you find yourself. Either way, there are many camp sites all around Britain where you can stop overnight. Most sites are surprisingly modern with facilities to hook your motorhome up to electricity, water, toilets and gas. Most sites now have a central building with showers, laundry, a shop, bar, restaurant etc. Camping sites are well-marked on almost all road maps and they also indicated along the road by Brown Signs (tourist signs which are brown in colour).
Road and town/city maps are easy to find in most newsagents, supermarkets and service stations around the country. Compared to somewhere like Australia or the USA and you can reach most places in the UK in just a few hours. Wherever you are you will have no trouble finding maps and overnight campgrounds.
Do bring lots of money though. The UK is one of the most expensive countries in the world and the cost of food and fuel has become horrendous. If you are travelling for a couple of weeks then you will spend a great deal of money fuelling a motorhome, especially if you are used to the low cost of fuel in the US or Australia (they might think their fuel's expensive but it's nothing compared to here!). You might like to bring a coat too as the UK is known for it's rain. The wettest month of the year is August but we do get lovely weather too - it's just pot luck.
Hope you have a great time.