I agree with nas-1. And if you already have two desolations, I think your best bet is to go dual desolation, like nas-1 said.
Get a magma recoiler or a couple repulsors (if you use repulsors, don't upgrade them, in my opinion, unless they're the advanced repulsor, which is premium I think).
Or a hammer and terror cry.
Basically, two weapons to push your enemies to your 4-8 range so your desolations can kick butt.
Also, work on your modules. Your target goal should be at least 500 energy capacity, 500 heat capacity, 250 regeneration, and 250 cooling.
Unless you plan to go energy-free. See the META thread for long-term ideas:
I would also max your savior resistance and iron plating. These work for lower ranks, but don't ever get rid of a platinum plating or any of the premium resist modules and/or fortresses, if you get them.
In my opinion, energy/heat engines are superior at lower ranks than heat storage / energy storage. Combined storage units are good.