LST, Large Stationary Target. They were very slow and a prime target. Also if i remember right they had some issues with reefs and only being able to be run in during certain times of the tides? Add them and most enemy cons will have a field day shooting them worse than they do with pt's and lvt's now. Then again the thought of being able to sneak some tanks in close has it's appeal. 
Make them as hard as curent VHs.
Meaning make them so it takes the same amount of ord to destroy.
Could mount some guns on them for protection. but its primary protection would ammumingly be from the carrier based aircraft and from the GVs themseves. as well as from the ships main guns.
Pts could also escort them in.
It would add a whole new dynamic to the Cv game and certainly give basetaking from a CV more of an invasion feel.
Right now the HE shooting LTVs are inadequit particularly when facing enemy armor and hardly ever used cept to bring troops ashore