1966 has a serial number, not a "vin"
1966 serial number examples....
J0266124 JI286824 S0226534 SI246158
1ST Position S (California) J (Jackson Center, OH.)
2nd Position I (International Model) O (Overlander, Land Yacht Model)
3rd & 4th Position Length (22 = Safari)
5th Position Model Year (6 =1966)
6, 7, 8th Position Sequential Production Model. (Over 500 Double Bed, Under 500 Twin bed.
Look for a number like JO226123. Same as number on title.
Some say that it can be found on the tongue/A-frame, but I scoured my '68 tongue area and didn't find it.
If it's not on the plate by door, you may not find it.
Good Luck