We get this one a lot, the long and short of it is that the Forrestal there has to be the same size(or greater) than the Pilumnus class to support opening a rift of that size. The cheapest way to do it would be small cargo holds. To clarify, the warning told you that "at least one ship is larger than the ship", and thats the important part, the transit rating of the Forrestal is 14,450 tons, not 37500 tons.