I have added <option name="isLandTransport" value="true"/> to train and <option name="isLandTransportable" value="true"/> to aagun, field_gun, heavy_gun, gas, infantry, cossack, stromtruppen, colonial, big_bertha and conscript.
And I've got this one.
UnitAttachment are either misspelled or exist only in a future version of TripleA. Setter: isLandTransportable
I am using triplea 1.9.9.07621.