OK, so here's the question - When I wrap over the underwrap, how do I keep the new wrap from slipping into it? This is my first offshore rod, so this is a new one for me.

Flip your rod end for end around so you are wrapping over the under wrap in the oppisite direcition
Good luck Bob

Make all your underwraps in their proper position according to guide placement. Apply a coat of epoxy, let set for a few minutes then wipe clean. After sufficient drying time make your guide wraps as usual over the hard surface of underwraps.

I always used D over A and used a coat of color preserver on the underwrap before making the overwrap. All these suggestions sound like good ones to me.

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When I had my shop on Maui, we did almost exclusively offshore rods. On double wrapped rods, we used size "A", either regular or NCP for underwraps, with the guide wrap being "C" or "D".
On triple wraps we used "A" regular for underwrap, then "A" NCP for the first guide wrap, and "C" or "D" on the top guide wrap. The "A" NCP threads were a little larger in diameter than the "A" regular thread.
In this way the thread laid well over each other and did not appear to have that bulgy look. Tried to keep with the wraps matching the rod taper as much as possible for a uniform look.

Size A on the underwrap and a light coat of finish, followed by double wrap on the large guides with one coat of finish between. This way you can still use A thread and then final finish coat. The smaller thread diameter of A also one can defend by more turns, so the same amount of thread , thus just as strong as C or D.

Rich
Solyrich Custom Rods

How long Should the Over-Wrap be?
Is it the same if using "A" or "D" Sizes of Nylon Thread ?
THANKS !

Thanks for all of the advise. I didn't have any size A in the color I needed for the underwrap, so I did the CP trick. I think I'll probably stick with that method, regardless. It worked great.