What if there is not enough room to install automatic foundation vents from the outside?

It may be possible to push the vent in from inside the crawlspace.

It may be possible to push the vent in from inside the crawlspace, facing the correct way. You should then be able to "rock" the frame in place from the outside. Note: You may or may not be able to use the clips that come with the vent installing it this way.