You can use regular rubber grommets such as used for electrical pass through. Whether one or two holes is up to you -- what's easier? You can also use a bulkhead connector (plate), but would have to cut the hoses and put screw-on ends on them to screw to the connector. Something like this: Inline AC Bulkhead Plates with Fittings - Speedway Motors, America's Oldest Speed Shop
. Some companies make a two line connector (check Vintage Air), Speedway only has the four line (AC and heater hoses).