The Mosh's do a great job but if you want to do it yourself there are some covers out there. If you didn't know the YTM 200, 200E, and 200ERN (all Yamaha 200cc trikes) use the same seat. Here is one that is on ebay, not the cheapest but not too bad either. If you have a sowing machine a time you could make one for less then $10 worth of material. The way the YTM seat is you will need to sow together a few pieces to get it too fit right. My brother made the one I have on my trike. Anyways, here is the one on ebay...
http://cgi.ebay.com/ebaymotors/BEST-...spagenameZWD1V
1984 Yamaha YT 60 Tri Zinger(current project)
1983 Yamaha YTM 200 (rear suspension kit)..... long term project
2004 BMW R1150R
1972 Honda CT 70
2007 Lifan 110