I live in Kanchanaburi and got my bike and car licences last year. In addition to what George says I also had to get a certificate of residence (one for each licence) from immigration, about 20 mins, B500 and a health certificate from the local hospital, also 20 mins and B500.
At DLT I had to watch the road safety video, 1 hour. In all it took about 2 hours in DLT
I have full UK car licence, which is also a provisional bike licence and had an IDP
The second time was about 6 months ago, when I drove from Kanchanaburi to Ban Laem on the Cambodia border. I drove into town parked in the main Square and walked over to immigration, about 100m. Left Thailand and returned about 30 minutes later. Easy as that, no problems at all. Ask at the Thai immigration on the way out for a new TM6, the guys in no mans land between the borders have them, but will want a huge amount of money for one (they do fill it in for you though)
I have done this twice in the last 18 months. The first time I drove from BKK to Mukdahan. You can't take your car into Laos, but there is a managed pay car park a short distance from the bus station. I got the bus across the bridge to Laos. I then got a taxi to immigration in Suvannakhet. {I got a non imm O, took 2 days). You will have to haggle with the taxi as they will try to overcharge. I arranged with the taxi to pick me up from the hotel the following day to take me to immigration to pick up my passport and then on to the border. Got the bus back to Thailand and picked up my car and drove back to BKK.
I had a similar problem many years ago- it turned out that the culprit was biological washing powder. There are enzymes in the powder to make whites shine, the problem is that many people are alergic to them.
In my case I changed biological powder for soft soap powder, washed everything 3 times and the itchy rash disappeared.
You will have to provide proof of where you will be staying and for how long in each place.
Me and my wife went to UK for a month in 16 for the wedding of my daughter, we stayed with a friend in London, then a hotel in Norwich and then on to Scotland.
I got a letter and passport copy from the 2 friends I stayed with and included a copy of the hotel reservation and a copy of the wedding invitation.
Be familiar with the details on the visa application. When we arrived at Heathrow I went though the non Brit channel with my wife. The IO was very friendly and chatty, but with a purpose. He was asking in a conversational way about info we have on the application. We hadn't BS about anything, so it wasn't a problem. I presume he was looking to see how I answered his questions