Herman
A 6x12 is about the "right size" for the RTV. Be advised that most are rated at 3000# gross so you'll be right around that mark with the RTV on it.
Don't worry about the RTV. Mine is now 11 years old. It's never been in the shop but it doesn't have bordercollie hours or a snowplow attached.
Haha Zoom, Only my 05 went in the shop for warranty work way back in '05. Most work you can do Herman ... if I can do it you can do it . collie