Smoothing rough primer and paint recommendations...
 

The stripped tub I have has this insanely rough primer on it. What is the commended method to knock that roughness down? Primary area of concern is the interior. Hope I can find some power tool method. So many curves...

Also, what is a good durable paint? I've previously painted with single coat glasurit and that stuff is great, but just silly expensive (I know, you get what you pay for). Want something that will hold up on race car and would prefer a single coat (ie: no clear coat) type paint.

For durability, you can't beat the two-part urethanes, I don't think, other than powdercoating. I have heard good things about Endura: http://www.endura.ca/automotive.htm

YMMV,
TT