So here is my problem. I tried staining my new fiberglass door, using gel stain, in cold wind. The result was horribly blotched. After a lot of searching, I decided to remove the stain and try again fresh. I used CitriStrip spray, plastic bristle brushes, a lot of elbow grease, and a little pressure washing to help return the door to its original, unstained state.
Now, my door looks pretty much like it did new except for one important thing; the thin primer that was originally on the door has been partially removed, more so in some areas than other areas.
I want to restain my door, but I’m worried that applying gel stain to my unevenly primed door will give me uneven results. I think I should re-apply some primer, but I have no idea what kind of primer I need. Do I even need to worry about the primer, or will several applications of the gel build an even amount of color?
Your caution with regard to staining over a bad surface serves you well. Not to worry, you are on the right track.
I am going to assume you are working on the exterior side of the door. Use an exterior primer, oil or latex should work equally. Try your local paint store (not the mega-store) and ask for a primer tinted close to the original base color. The professional will probably tell you he or she can not guarantee the primer to be a match for the color chip. That's alright, it does not have to be perfect. Then prime away and try to stain in a little more moderate conditions.