Zelderex is a game about numbers. If you can't, don't, or won't understand that aspect of the game, your hopes of coming out on top are very slim. All the numbers you need are presented for you in the game.
Bombers are only used in the game to destroy buildings in the most fuel efficient manner. Bombers do a full 200 damage to buildings instead of the 10% that normal units do.
If your Bomber Runway is destroyed, you will lose any bombers in your base. However, you do not need to have a Bomber Runway to store your Bombers. Once you're finished attacking your enemy and you want to log out of the game, you can use the Unit Transporting screen to send your Bombers to another base without a Bomber Runway. Once there, they cannot be destroyed unless the entire base is destroyed. In addition, if you do not have a Bomber Runway in your Homebase, any bombers would be 100% safe their since you can never lose your Homebase.
Using Bombers can be a little frustrating if you're not careful. You have to be sure that you have destroyed the Anti-Air Turret in the enemy base before sending in any bombers. You will have to use regular units to achieve this. In addition, if the enemy base has a Shield Emitter, you would need to destroy that with regular units before you can destroy the Anti-Air Turret.
The first thing you will want to destroy is the Defense Field, so that your bombers do 300 building damage each instead of 200. Try to ensure that each attack destroys a building, since you only get 20 attacks on a given base per day.
Scrap Bots allow you to recoup up to 50% of the value of a unit that is lost, in the form of money. This means that if you have 100 units and Scrap Bots of a high enough level to recover the entire 50%, you can rebuild 50 units essentially for free when those first 100 are destroyed.
If a unit is equipped with a Scrap Bot that can return more than 50% of the value of the unit, the excess ore collecting ability will be used only if excess ore is available. For example: if Unit A costs $3,000 to build and is equipped with a Scrap Bot capable of collecting $2,000 in scrap, when Unit A is destroyed the Scrap Bot will only be able to return $1,500 in scrap. Now add Unit B which costs $4,500 and is equipped with the same Scrap Bot capable of collecting $2,000 to the equation. Unit B when destroyed produces $2,250 in scrap (50% of the value of the unit) and the Scrap Bot returns only $2,000 of that scrap. Unit A’s Scrap Bot returns the $1,500 from Unit A and picks up the excess $250 from the destroyed Unit B.
After you research and purchase a component, you can attach it to a unit. Once attached, the unit will not cost any additional money to build. Modifying units that are already built will cost additional money per unit, so be sure to design your units before building them.
Components are more effective the more you can send into battle. This means equip them onto the lowest level unit you can to ensure you can buy more of said unit with the component on them. For example, if you have a +100 damage component on units costing $4,500 and $9,000. You would get more benefit from the $4,500 units since, for the same money, you would be going in with 2x the number of components. This holds true as long as the more expensive unit does less than 100 more damage than the less expensive unit.
Winning in combat is simply a game of math. If your losses are lower than the enemy losses, you win. Currently in World 2, Land units are the only reasonable type to use for unit combat. The Hit Point, Attack and Component per Cost make them superior to the Hover units. Air units are used mainly for scouting (but if you get good components on them they can be very decent fast fighters).
One strategy to achieve victory is with two units; a Defense unit and an Offense unit. For your Defensive unit, you want to add Combo Shield and Scrap Bot components to a lower level Land unit that the Scrap Bot can return the full 50% value of when it is destroyed. This way you achieve the maximum amount of Hit Points for the minimum amount of cost.
For your Offensive unit, again you will want to use a Land unit, this time a higher level version so that the lower level Defensive unit will be destroyed first during combat. The component you will want to add to this unit is the best Combo Weapon you have researched.
This Offensive unit will provide the maximum amount of firepower for the minimum amount of cost. The Offensive unit's Scrap Bot does not need to recover the entire 50% of the unit's cost if your Defensive unit Scrap Bots are able to return extra ore.
Once you have your unit creation done, selecting the right mix for the job is easy. Once you scout a base's units, you have the values of both their Attack and Hit Points. First, divide the enemy Attack by your Defensive unit's Hit Points. Round that number down and you have the number of Defensive units to send.
When you know how many Defensive units to send, you can figure out how many Offensive units to send in to clean up. Take the enemy's Hit Points and subtract the amount of damage your Defensive units will produce, and then divide that result by your Offensive unit's attack value. Round this number up to insure the total destruction of your enemy. You now have the proper unit mix to minimize your own loses, while maximizing your enemy's.
The only weakness to this strategy is how to defend your Offensive units while they are stationary at your base. The way around this problem is to make sure you have enough Defensive units with Scrap Bots to ensure the full 50% of your Offensive units' value is returned and you will give as good as you get.