Took my car into Laos last month, we had all the forms but for some reason, Thai Immigration did not like them, we had to re-do them, plus had to get tons of photocopies made. Took over 1 1/2 hours to get into Laos. No hassles with the police (this time...). We also parked the car overnight at the new train station in Vientiane as we went to LuangPrabang, it was perfectly safe. Would I do it again? Probably! I wish though that with ASEAN, travel by car was made easier! It was very convenient though to have a car in Vientiane, for shopping and sightseeing etc. Tks OP for all the advice, very helpful and much appreciated.