My parents is 45x10 and has gas central heating, proper bathroom, plastic covered metal tiled roof, dishwasher ect ect.
Theres is called a mobile home
Yep, nice, I suppose ours is called a mobile home (or holiday home) as well, gas central heating, double glazed, en suite to the master bedroom, separate shower room with toilet but unfortunately no bath, pantile roof, lounge has free standing furniture, french doors and we're hoping this year to install a veranda so that we can use them properly. Kitchen has full sized cooker, fridge and washing machine, proper 'home from home', even the dog loves it, probably because she gets a lot more walks there than she does at home. 
There are 3 basic type of caravans
biggest are mobile homes, which are permanent residential homes, from companies like Tingdene, Neve Valley and such I remember that NV were aluminium green/white, another make was yellow white and my parents Tingdene is chocolate/cream rendered wood.
Commonly available as double units up to 45x24, or even a quadrupal unit I saw under construction at TIngdene of around 60x20.
NExt down are the static holiday caravans, usualy cheaper made than mobile homes and also smaller - makers like Willerby and PEmberton, usually found in flocks at Brean and Porthcawl.
The final category are touring caravans which are twoed, they are the only ones with suspension and brakes and Swift, Bailey and Lunar are well know makes.