I would suggest our FL 843 blank. This is an all glass blank and are perfect for downrigger use. Hope this helps.

Here are the 3 I built and use for kokanee and trout, since you catch both with similar lures here in colorado, specifically blue mesa in gunnison.
FL9041
GFW932UL
IFW842UL
Koks are tough to land compared to trout. They spin around and around trying to get leverage to tear hooks loose.
The idea is with a super limber long rod it will be hard for them to get slack line.
The fiberglass fly rod will bend down and touch the water with out popping release if you want it to when you set downrigger.
When they pop the release I never stop trolling since you are going so slow. Then we stop to fight fish after I am tightening line up.
The feel is completely different with all 3 rods.
Honey colored fly rod is conventional setup, which is a gorgeous rod.
Others are spinning.
With all of them the blank bends all thru the handle cork.
The fly rod has the largest amount of bend is the most forgiving.
You start having a quicker rod load up with gfw and a little more feel, if thats the right word.
The IFW does not bend near as much, it is a little shorter, but has a bit more back bone, but not much.
The super line goes on spinners and flourocarbon on conventional.
My son is more of a bass type fisherman and he does not like the soft fly rod feel. He goes for for the IFW. I need all the advantage I can get and go with the longer soft rods.