The basic course is just that, VERY Basic and really only just covers the minimal.
You would then need to get on manufacturers courses for the equipment, all of which cost money to do.
Then the electrical test and inspection courses at around the £600 each mark, then Gas ACOPS at around the same costing.
Then the cost of tools, test equipment, vehicle, spares,Insurance etc
And at the end of all that, you can only work on caravans out of warranty.
To be able to work on vans still in warranty you would have to go down the Approved Workshop route with C&G in Caravan Engineering and all the things associated with that.
Expect it to cost a minimum of £10,000 to set up properly.