METAL POLES, GIRDERS AND SHEETS
Come in a few varieties, varying in thickness, strength and decay, and can be made of either steel or iron (unless we get a metallurgist of some sort later on) all of which affects the weight.
Whatever that Scrap was used for will affect its function: for example
chickenwire sheets and if you roll your minimum score in an action using scrap, it will deteriorate or be destroyed.
POLESBill can wield poles effectively, even heavy ones. He can't battle up close very well, but he can use LIFT to force enemies back with whatever he's holding. Poles make good weapons, but Girders are much better at pushing foes. Poles can be used however you use your imagination. Strikes from the pole come from your LIFT and FIGHT stat so he does a decent job with it. You described that Big Bill gets over-exerted, so Poles are ideal because they are usually light weight.
GIRDERSHe can also wield Girders as spears. He can only strike 1 crab at a time (right now) and use it to ward off enemies by swinging it around.
This is not a FIGHT move, enemies are deterred, but only cus you're swinging around a huge steel girder.
LIFT attacks can be good surprise attacks and can occasionally hit enemies situationally. Mostly it's crowd control, like using the girder to push a row of enemies. Again, this is LIFT so it just pushes them back (for now, he'll get better with more effects such as stun, or damage)
Waving a Girder tires Big Bill and exerts him cus he's a tiny crab. Maybe it stresses his heart. Still he's better at LIFT than other anything else.
SHEETSBig Bill, due to having a gnarly LIFT! Can wield the sheets as barricades and walls to block off enemies in combat. He can form a roof against air attacks and should plan around the natural terrain and position of the truck/crabs.
He can use them to do LIFT attacks which don't do much damage but can be defensive (the sheet would have to be appropriate thickness and material to be effective),
He can also use his FIGHT skill to deftly wield thin sheets like huge playing cards, slicing up enemies. I think we can all agree that a huge crab waving around a metal sheet and slicing shit up is cool.
All crabs can do these things but their lifting power comes from LIFT: If you have low LIFT you can probably still use thin poles and sheets as weapons, but not more than that.When they FIGHT with it, they use FIGHT skill to determine the effectiveness of combat.
FIGHT and LIFT are distinct skill and have separate functions. Knowing how to use FIGHT and LIFT together can change the tide of combat.
When combat goes sour, form up, get the truck on the road and swap to DRIVE.
Using the right skill at the right time will save your life, but what about the team-mates and cargo. Think how to protect the valuable shit.
Big Bill, since you have high lift, you are in charge of protecting cargo, and you can save crabs by throwing them long distances.
If you choose throwing specialty, you can throw harder and further.
Throwing comes from
LIFT: You can throw poles, girders, rolled up sheets etc. as well as crabs and cargo and anything you can think of.
Use your imagination and be a crab that the Crab Goddess sent into the world as her trucker, to make sure everything goes alright. Big Bill seems like a humble sort of person and genuine nice guy. If you want to make him mean as coot but deeply caring, write it like that motherfucker.
For anyone with weak LIFT, they can still throw light scrap relatively far.
WELDING
The use you make of these also comes into effect on the truck when choosing what you want to attach. Maybe I'll make the ability to do welding dependent on fuel and appropriate equipment which you would keep and be resonsible for. It's also reasonable that you and the crew could use that fuel as a makeshift explosive device for emergencies. Obviously it is a valuable and rare resource and you don't want to waste it.
Welding is mainly used on sheets, but use your creativity. You can create rudimentary objects at first.
OTHER CRABS: You could also use these crowd control options by using LIFT! but not as effectively. Again, surprise attacks with LIFT are much easier than doing frenzied battle and it's unlikely to hit.