The Roller base was underestimated for the first time I see it. Run fast, but can't shoot after moving, 8HP means it's not a mobile shield.

Then, we notice it has +1 range, and +2range,3dmg at 3.0 upgraded.
Those ranges means it can work as a "mobile gun position", and +3dmg for machine guns that strikes multiple times.

The problem is, it's range does not compensate it's drawback. We need some cover on it. But when those energy and guns was spent on this gun position, the firepower of those escorts is not strong enough to keep monsters away, especially those fast or long-ranged guys.

If the drawback cannot be avoided and escort don't work, let's try do something with range.
+2: Roller 3.0
+1: Ranger as body
+1*2: Eagle Eye as "escort"

In this way we got +5 range in total. What's that mean?
With a weapon of range 2, we can hit that DEMON boss from the baseline!

Transport:Mini Walker
You can choose 8 transport part to drop, it's easier to get our Roller and we don't want it at the beginning, until we get +2 range

Body:
Eagle Eye, Ranger

Weapon:
Double Double: Good starting weapon
[optional] Smoke Grenade:
At beginning we can use it to limit some monster's mobility. Grant some chance to grab more energy before eliminating all monsters.
Later we use it normally as it should be used for. It's normally range 2, without range bonus it's almost useless. But now we can suppress from far-far away!

Just pick what you want except those funny choice for artillery.
Usually we don't need armor, 1 healing tool is enough, get Gatling of course and whatever dmg boost stuff.
Armor build can still work, use Defender or Impervious body part. But the firepower will be limited, and roller only have 8HP. Be careful, losing one of these mobile fortresses could be expensive.

Secondary choice to Gatling is Cannon, because we now have chance to stack those armor breaks.

We might want some covering weapons, such as landmines while pushing forward or freezer (or BIG ROCKET if you wish :) for last defense.

Get your range boost, kill everything in sight, move to the edge of enemy attack range, repeat.

Range trick:
In second or third map there are monsters trying to stay out of you gun range and seek for chance.
This includes Air Strike! If you have air strike on artillery, they will keep 1 more tile away from your normal 2 range weapons

1. Move Eagle Eyes away after all payload has launched. These cowards will measure distance without Eagle Eye bonus.
(Not sure if this really worked)

2. The AOE of explosives does not count.
Smoke grenade might not do dmg, but you can smoke from artillery, then let others move forward.

3. If you really got Air Strike, use 1 and 2 together

Here are some examples showing the strength of this build

(Note: Need some luck, if you brought Doctor and encounter cloak in 2nd map. But smoke is enough to suppress those annoying bullfrogs)



Suppressing from afar, then it is possible to take an elegant walk to the energy point.



Fighting a boss is even easier than pushing forward
(Might suffer some lost against the infinity range line attack boss)



Long range suppressing, they can out-range anything



Smoke grenade 3.0 have 5 AOE damage, offer some landmines together to cloaked cowards.