We took a double jogger for our most recent trip. I couldn't find a rain cover made specifically for it, and the only one I could find that said it would fit was $70 plus shipping, so I became ambitious and decided to make one myself.
Suprisingly, it was very easy (took me less than 1 hour to make it) and it is custom fitted. I even added red ribbon trim with white polka dots to give it a Disney look.
I started with a clear shower curtain liner, some elastic, a lingerie bag and the ribbon trim. I laid the shower curtain liner over the stroller, folded it where it needed to be folded to give a good fit and pinned it there to mark where I would make seams.
I also marked where I would put elastic around the bottom and the handle bars.
Then I marked with sharpie a place on each side for an air vent and cut those places out.
I sewed the seams, then sewed ribbon trim over them. Sewed in the elastic and cut squares from the lingerie bag to sew in the side holes I made on the side for air vents.
The rain cover came in quite handy for our trip June 1-9. Lots of rain that week, and it worked perfectly. My seams weren't perfectly straight and I wish I had sewn the ribbon to lay better, but for less than $10, I had a custom rain cover.
I should add, that I am not a seamstress. I do embroider, but other than adding trim to things and hemming items, I have never sewn anything (though I hope to learn).
So even if you're not a great sewer, but have access to a sewing machine, you could make a rain cover if you're having trouble finding one that fits.