There have been some instructions on how to sew tunnels in the last couple of years. If you want to wade through them, search for "tunnels" (without the quotes), start about two years ago and work up from there. Sorry I can't remember who posted them.
I used a dish rack I got from the dollar store.Then I zip tied the fleece. The space is wide enough that pigs can't get stuck. To wash just cut the ties, and throw in the washer! It's great for lawn time
When I made mine, I doubled up (so it would be 2 layers of fleece) a long piece of fleece in a rectangle shape. I made it super wide and long so I could roll up the edges.
So, I doubled it into the two layers and folded it in half. Then I sewed the two edges (the raw edge to the fold) together to made the tunnel. Then I sewed a strip of boning to the two openings and folded them (made like a cuff) so they would stay open. I was bored so I just hand-sewed it. Didn't take long. I am horrible at explaining so I hope you understand! I also have a bent grid tunnel that works wonderfully if you don't want to sew!