This was your first contribution....
"By law, a foreigner in Thailand must carry passport on their person at all times.
In practice, when checking into hotels and am asked for "passport", I just hand over Thai driver licence and that has always been enuf."....
Which means nothing in regards to the OP.
The guy is going on a one month trip involving an island and driving a car.
To not take passport is insane.
Then you type about checking into hotels.
Check in is of little/no concern.