The migrants suffocated in the sealed container en route from Zeebrugge to Purfleet in October 2019.
Eamonn Harrison, 24, who dropped off the trailer at the Belgian port, and people-smuggler Gheorghe Nica, 43, were convicted by an Old Bailey jury.
Two others were convicted of being part of a wider people-smuggling conspiracy.
The trial examined three smuggling attempts by the gang - two that were successful on 11 and 18 October, and the final trip on 23 October.
