google cipa mirrors.com they have a big selection, including some that slip over the exist mirrors, and extend out. i have them for my Surburban. out on when towing, remove when not.
I am fortunate enough to have pretty big mirrors on my truck to begin with. I use those 3.5" round blind spot mirrors that stick onto the side mirror with 3m tape. They work really well for I use them for. Best $4 I ever spent on that truck. Obviously if I was towing something bigger, it would be different.
Thanks fellas. I went ahead and purchased a couple of the cipa universal ones that slide down in next to the window so we'll see how they work I guess.
Like $44 a piece from JCWhitney....They may be overkill, but for the WJ series (1999 - 2004) I couldn't find custom fit mirrors. And the other universal mirrors said for 7" - 10" mirrors and I wasn't sure if my mirrors fell in that range and needed to get them delivered before Sat. They got good reviews on a few different sites so I bit the bullet.