I haven't played the SFC 1 Romulan campaign yet, as I prefer thee Federation & Klingon campaigns.
Suggestions:
Make use of shuttles programmed to attack when dealing with the enemy ships.
Find & beam up spare parts (magic screws) from planets to repair your ships.
Use hit & run marine sabotage attacks on the base's transporter & nastiest weapons.
Wait until you have better ships in the campaign before doing this mission.
Add TNG Romulan ship models into your game and use them in the mission.
If the base is Gorn then winning isn't an option.
In the campaign missions, sometimes withdrawing from the battle, after inflicting damage, is the winning move for the mission.