Hobgoblin Wagon Masters

Invented by goblins during the lost era and then refined many times over since, Goblin Wagons are made for war. A squad or platoon of wagon masters make the best of these wagons and with their training they are a part of the war machine that makes a goblin war master so very effective. The entire wagon is crafted very carefully with precise openings drilled very carefully. All of the wagons are made to exact measurements so that wrecks can be salvaged and then used together to make functioning units out of damaged ones. It takes a set of metal smiths and carpenters working together to produce one, normally if a warlord is going to march and has goblin tinkerers in his ranks then a team of carpenters and smiths is assembled in advance to make as many of these as possible.
The wagons are heavy with iron or steel bands placed on the wheels and solid steel axles. There are no nails in the wagons. Everything is held together with steel pins that have holes placed in them which in turn have wood or steel pins placed in those. Pegging, Mortise and Tenon joints, and biscuit joints. These can slide together and hold well and then having removed the pin or having a lever placed in the join can be pulled apart again later. The frame is made with three by fourteen boards. and the top then has a thick tightly woven canvas that goes up on a bendable wooden fame made from wood treated the same as the wood used to make bows. The buck board is the one odd man out being a three by twelve and having no other matching boards. The center of the wagon bed is a stout twelve by twelve plank. The rest of the bed is made up of two by fours. When the back board of the frame is removed all of the boards that make up the bed of the wagon can then be slid straight back and out. The harness tongue that the horses, oxen, or other creatures that pull the wagon are tethered to is also steel.
Usually a team of six great horses or draft horses as they are sometimes called pull it or four oxen. This is required to make up for the weight of the wagon. The squads that run these wagons are usually made up of six to eight individuals with a bugbear almost always being included in the group for heavy lifting and to help push if something happens to one of the animals. These teams know all of the configurations for the wagons and the positions for creating each one. This includes having at least one member free to watch for attacks while the others work, usually trading off a heavy crossbow as different members are needed for various tasks. No configuration should take an experienced and uninjured crew more than three minutes to assemble from any other configuration.
Configuration examples:
Watch Tower: The wheels and axles are removed from the wagon and the frame is lowered to the ground. Two of the wheels are aggixed to the frame with the buck board being brought back to then create tension for the attachment of the axle to to the buck board. Rope is then used to help with tension and stabilization. The second axle is then attached to the top of that won using a pin and biscuit joining between the two where the wheels normally fasten. The boards from the bed are then pinned into a frame with the canvas stretched tight almost drum like around the frame. The remaining two wheels are lashed together under the canvas supporting the outer frame of this new box. All of this is lifted by rope and pulley using the plank as a lever to the top of the axles and fastened in place. The wagon now acts as a lookout tower with elevated archer and visual position.
Catapult:This is one of the easier configurations since it keeps all of the wheels, axles, and frame in their 'wagon' position. The plank makes the main beam of the catapult, the rest of the boards and buck board are lashed into place to allow the main beam to pivot and the pulley system that is kept with the wagon is used to create the tension for the launching arm.  If the area is unstable or they expect to be in place for a time then the wheels and axles are removed to create more stability.
Shell: This is the least liked by the crew in actual combat because is often leads to the destruction of their wagon. Given the amount of time that each crew spends caring for their wagon and working with it they are usually very attached. The buck board and tongue or removed and the canvas is placed as extra padding on the underside while the frame is inverted creating a box on two wheels. The front of the frame is removed and placed between the axles for stability and the pins are all placed in each opening of the axle so that hand holds can be created. The wagon is then used as shelter when approaching enemy defenses.
Two or more wagons can be used to make a siege tower and depending on the choices and tactics preferred by the leader of the army there are several other configurations that can be built in to a wagon. However many rule others out because of the placement of the needed openings and pin holes. As a result there is no wagon to date without magic that can do more than six configurations.
A good team of wagon masters usually has to train for a year and should be able to affect minor repairs in the field, making them soldiers who are also craftsmen. The understanding and skill level in carpentry or metal work makes them much harder to train and more expensive than the usual military units.