I saw a pretty cool instructable about making a fabric gig bag that would probably be pretty easy to modify for a mandolin using the same principles. You could probably waterproof it and seal the seams, too. There are a lot of simple ways to waterproof stuff you might also find.
have you seen this link
http://www.doityourself.com/stry/how-to-make-a-mandolin-case#b
You could cover it with a ton of different materials for waterproofing too depending on your tastes and personal preferences, costs, etc.
http://www.doityourself.com/stry/how-to-make-a-mandolin-case#b
You could cover it with a ton of different materials for waterproofing too depending on your tastes and personal preferences, costs, etc.
I use a padded racquetball racket soft case like a gig bag. My POS A-style fits perfectly and it even has a zipper pouch for strings and sheet music. Been using it for a few years of hitching and freight-riding and it's worked really well.