In the past, I've recovered a few seats using the old IROC Camaro T-Top storage bags. It's a sort of stretchy type vinyl with a fleece lining and it's very easy to use. It stretches well and is easy to get all the wrinkles out. Looks like a brand new seat when done, but I guess those T-Top bags are probably getting hard to find now.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.