Hi Blowin,
As Cas -Galway mentioned, you can make a paravane out of plywood and tin / Aluminium at the correct angle for depth at the front.
However I use an 'Eddystone Trolling Paravane', purchased on-line from Marine Web Store Ireland at a little over €6. It works great with an Eel about 1.5 to 2 meters towed behind it, especially close to the rocks. I could honestly say it has never failed me and I have caught some great Pollack and the odd Bass on it. No Salmon or Sea Trout yet though, but I'll keep trying.
Here is the link to the web page for the Eddystone Paravane and good luck.
http://www.marinewebstoreireland.com/#/ ... 4551809006