Help for a son's costume

I have a 5 year old son that would really like to have me finish his boba fett costume that I started 3 years ago. (I know, I know, I'm slow). Here is where I am at. I have the armor, but it still needs more painting and weathering. I have a pattern for the jumpsuit. I have material but I think it may be too heavy and will use it instead for the vest. I have printed out the gauntlet and backpack patterns at 66% and have started cutting the gauntlets from a for sale sign (light weight sintra). I am planning on making a majority of the backpack out of foamcore board. I saw the tutorial for the belt with boxes and tools, so those shouldn't be an issue. I need help with a few things, though.

1. I have a rubies boba helmet, but it is warped so that it is oblong front to back, rather than circular. I have tried heating it a little and putting a ball inside it to help retain it's shape as it cooled, but soon after removing the ball, the helmet returns to the oblong shape. is there anything that I can put in the helmet permanently to help it retain its shape?

2. What would be a cheap, but sturdy way to make the girth belt? I can dye it if need be and saw the tutorial on dying it using latex stain, but I need to have the belt before I can dye it.

3. Any help with weathering would be great.

4. What is a good inexpensive way to make the shoes? He will outgrow them too quickly for me to want to put a lot of money into them.

The best thing about all of this, though, is that I have another son age 2, who will get to wear this when his older brother outgrows it.

thanks for any help you can give me.

Pics of the helmet would be helpful. I used TK409's method for my sons belt (TK409.com Do-It-Yourself Star Wars Props). After I ran the needle and thread through the ropes, I braided some old hockey laces to stitch to it in order to make it look more like the real deal. I don't remember what color stain I used on it but it looked pretty descent when it was done. I used flat black paint, misted, for weathering. For the shoes, we used some old white converse we found at Payless Shoes and I painted them light grey and black. Obviously this isn't correct but worked well. I choose no toe spikes because...a 4 year old doesn't necessitate toe spikes... Good luck!