In spite of the fact, that long distance VIP coaches in Thailand are faster than trains, they are not so fast, as they can be. Average 300 miles distance in such a coach will last about 9-10 hours. The main reason is too many stops. Even, if your route will consist of 2-3 stops in small towns, you also stop at rest zones and in petrol stations. But the main and the special reason of the inconvenience in Thai coaches is that in all long distance coaches in Thailand it is too cold. It is the Thai habit to cool down in hot and humid climate. Thai people do not like hot, so they decided to make all air-conditioned places as cold as they can be. In 99% of cases when you catch a cold in Thailand, it will be in air-conditioned places, and especially in coaches. Imagine your trip about 8-10 hours in the bus with the temperature averaging 13 to 17o Celsius.
Chilly recirculated air and inter mingled with periods of humid hot air mess with the bodies immune system.
Take with you any of warm clothes (coat and jumper)
Take anything, that you can use to cover yourself with (sleeping bag,mossie net,pillow scarf or a shawl)
Be sure, before travelling by bus, that the company has blankets in the bus
An XL hoody will be very useful (you can protect your eye's from the glare of passengers smartphones and enable you to sleep with comfort)pulled over one's face.
Take socks and never travel in Thai long distance coaches with bare feet or just sandals and in shorts.
However, flippers may be advisable in the toilet.
Another essential for the experienced VIP endurance traveller should be three large bottle's of Chang beer and maybe a sedative if you have a travelling companion to watch over your belongings.
Also if you are storing suitcases etc in the hold then a large padlock for your belongings as drivers and their mate's have been known for rifling passengers property.
Enjoy your inexpensive experience of travelling via the VIP bus in Thailand.......and don't forget the Chang