A simple DIY method is to use reflectix and plastic bags or aloksaks to add waterproofing. I use this for my camera, then again I'm probably carrying pennies compared to what you are packing.
I've had good luck with the relectix protecting electronics. I used it because I already had it. I guess another solution would be bubble wrap + some sort of plastic for water proofing.
At best...this could be a quick and easy solution until you have researched a more permanent solution.
EDIT: You could also cut foam to the right size for the padding. This seems like it would add more bulk, but offer a little more protection. I'm thinking of your lightest options here...they won't be stylish, but they will get the job done. Best of luck!