It's not difficult but you do need to know what you are doing to make sure its safe. Just because the hair dryer works does not mean it's safe. With electrics, we have several ways of preventing danger. If one fails, another will keep you safe. If 2 or 3 fail at the same time, your a gonner.
You are legally allowed to do it yourself. Caravans are called special locations in the IEE regs as they require a slightly different approach to a house.
You need a blue 16A plug and a socket for the hook up lead with a length of 3 core 2.5mm2 flex. Better still buy a mains lead.
On the Dandy you need a 16A socket inlet with pins not holes. Most sockets are socket outlets with holes.
Inside you need a consumer unit with RCD main switch and double pole MCBs probably 1 6A and 1 10A.
The earth must be connected to the Dandy chassis and the earth bar in the consumer unit.
Wire the mains sockets from the 10A MCB using 3 core 2.5mm2 flex, not the twin & earth house cable. It must be clipped frequently to stop it flopping about when towing. You can loop from socket to socket. Note that Dandies bounce around and the vibration may damage the cable. Houses do not bounce about. If any cable goes though a hole it must have a rubber grommet to prevent any damage. Mini trunking is good to cover it.
Use the 6A MCB to supply the charger or lights etc if you need them.
Having installed it all you need to test and inspect it to make sure everything is as it should be. I doubt you have the knowledge or equipment to do that but could possibly get an electrician to check for you.
The best sockets are Clipsal, made of polycarbonate, a very strong plastic. They will probably be coloured and will be sold in the better caravan dealers. They have round switches.