I don't know if it's a better process or not since you're talking about using Por 15 and I welded all the holes up but it's closer to the process I used 8 yrs ago when I kind of started all this hiding wires and smooth out engine bays
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In my case
Pull the engine.
Clean and degrease the entire engine bay.
Took a wire wheel on an electric drill and clean all the old paint off around near the hole you’re going to weld up.
Bought some 22 ga metal (20 ga metal is easier to find and will work also) to make some patch pieces just slightly smaller as the same diameter of the hole your weld up. Weld the patch piece into place. Weld and fill any hole larger than a dime in that manner (dime size and smaller hole you can weld closed by making a few passes to fill those small holes).
Ground down all the welds then use a body filler (all-metal ) to filled in any low spots in the engine bay due to either warped fenders, welding or grinding, spot welds, or any screw holes. When using any body filler always try keeping it to a minimum thickness by following instruction on the can or label. You’ll need to fill the low and uneven spots probably 2 or 3 times before you have enough buildup to sand the body filler smooth and flat. I used a long board and 4” sanding block to make mine as smooth and flat as I possibly could.
I found that if you buy the sand paper sheets for the body filler from any Auto Supply paint store your time spent sanding will be cut in half versus getting sheets of wet-dri course sand paper from your local hardware store, but that’s just me.
At this time you’ll also need to scuff the entire engine bay with a medium scuffing pad, and then clean the engine bay of any dust by either air or tack cloth.
Next prime:
Once the primer is dry you’ll need to sand the entire engine bay with 360 grit wet-dri sandpaper. After that you’ll need to remove any primer dust by either air or a tack rag.
Next apply finishing putty such as (Evercoat Glaze Coat) to fill in any small pin holes that the body filler or primer did not fill earlier. Sand the finishing putty with 360 or 400 grit wet-dri sandpaper, at this time if you see and small pin holes or recessed areas that you may have missed earlier or that didn’t fill properly fill with the finishing putty one more time.
Remove any finishing putty sanding dust with air and while doing that making sure at this time that you have completely eliminated all dust and any debris that could fly up during painting process.
Last and final time; tack rag the whole engine bay out, and now your ready to paint.
Believe me I'm no body man either!!