What a great thread!
I'm very much a DIYer too so this is right up my street.
As a very recent SIB owner my only contribution at the moment is my bow dodger, but there'll certainly be more to come! I've certainly taken some inspiration from you guys...
For this one I repurposed an old PVC groundsheet that I've had kicking around for years. Too many holes and tears to be used with the tent anymore so now it's gets a new life. I'll probably make up a few storage bags from some more of the scraps as well.