Like most RTS, the tactical variety of Sins can be well tracked to good old Dune 2; you have "tanks" and "launchers", short-range though units and long-range damagers which cannot last long. A standard WW2-like scheme. In space it seems a little weird: how can you create "fronts" in the void? It is more comparable to a naval than to land warfare. Naval warfare prefers versatility before single-purpose units, long-ranged missions, concentration on points instead of areas, limited observability of the battlezone lays higher needs on early warning systems. First question, why do we need to "entrench" ourselves? Leave that for Company of Heroes.
1.To make a "navalized" warfare, one first has to define how should a standard unit look like. The range of weapons isn't that important in the actual naval warfare; it is rather range of sensors and ability to discover the target before he sees us. For this we need at first a scout ship capable of uncovering the most adjacent systems. Such an ability exists in Sins - the plan is to make it general tool of tactics.
2.When you find the target, you need a weapon. But take the rocket frigates; why would you fire thousands of small, relatively short ranged weapons? A couple of nuclear cruise missiles sound better. Higher firepower needs also a better defence on the other side. We thus need not only the missile, but also an anti-missile defence. This can be done by following steps.
There are surely thousands of ways possible. One of them is to use a "frigate-creation" ability, like that of Sova carrier. You create entities for the ability, buff creating the new "batteries" (ie your missiles) and an entity of the missile itself. A modified Final Attack/Martyrdom, high speed (3k+) and a placeholder weapon changes the "battery" into a real antiship missile...
You need to copy and edit-
entities for the launcher platform (ship) and missile (ie CombatTurret)
AbilityDeployCombatTurret
AbilityFinalAttack
BuffFinalAttackActivate
BuffFinalAttackOnTarget
When your ship enters a system with enemies, you may launch the missiles simply by clicking or letting the autocast work. When they close to the enemy they are of course vulnerable to fire; you may solve this by using short-ranged vessels as well. The problem is they can fly between systems as well...a detail I'll have to solve yet 
They also can be aimed by hand, thus also change the target, if the previous one was brought down.
3. Fighters. You should have many of them. Every decent frigate carries at least a helicopter. You can set the size of squads variably and use many types of fighters for each side. Per ship it can be two types.
4. Finally, the ships themselves. You have a general limit of three weapons plus 2 fighter types and 4 abilities. A cruise missile as described in 2. counts as an ability. You may thus have 4 batteries of various missiles or salvos. Thus each ship can carry weapons for close combat, against strike craft and yet bombs or whatever. If the power of primary weapons - missiles - is set too high, the battles gain on dynamics, while the preparations and cooperation of units becomes more important than the economic warfare of amassing "tanks" (or Destras).
Well, it's a couple of ideas I try to realize (or have realized) ain my own mod. I don't expect it would get much interest, but it may inspire
